chore(samples): removing iot samples

[vishwarajanand]

Description

Removing deprecated IOT samples. Fixes: https://github.com/googleapis/google-cloud-php/issues/6727

Changes

1. Removed all fiels under /iot/src and /iot/test
2. Removed iot/composer.json and the phpunit configs
3. Removed GOOGLE_IOT_DEVICE_CERTIFICATE_B64 froms ecrets sample and the actual secrets file.
4. Removed iot from testing/* scripts

[snippet-bot[bot]]

Here is the summary of changes.

You are about to delete 25 region tags.

- [iot/src/bind_device_to_gateway.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/bind_device_to_gateway.php#L20), tag `iot_bind_device_to_gateway` - [iot/src/create_es_device.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/create_es_device.php#L20), tag `iot_create_es_device` - [iot/src/create_gateway.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/create_gateway.php#L20), tag `iot_create_gateway` - [iot/src/create_registry.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/create_registry.php#L20), tag `iot_create_registry` - [iot/src/create_rsa_device.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/create_rsa_device.php#L20), tag `iot_create_rsa_device` - [iot/src/create_unauth_device.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/create_unauth_device.php#L20), tag `iot_create_unauth_device` - [iot/src/delete_device.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/delete_device.php#L20), tag `iot_delete_device` - [iot/src/delete_gateway.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/delete_gateway.php#L20), tag `iot_delete_gateway` - [iot/src/delete_registry.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/delete_registry.php#L20), tag `iot_delete_registry` - [iot/src/get_device.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/get_device.php#L20), tag `iot_get_device` - [iot/src/get_device_configs.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/get_device_configs.php#L20), tag `iot_get_device_configs` - [iot/src/get_device_state.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/get_device_state.php#L20), tag `iot_get_device_state` - [iot/src/get_iam_policy.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/get_iam_policy.php#L20), tag `iot_get_iam_policy` - [iot/src/get_registry.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/get_registry.php#L20), tag `iot_get_registry` - [iot/src/list_devices.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/list_devices.php#L20), tag `iot_list_devices` - [iot/src/list_devices_for_gateway.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/list_devices_for_gateway.php#L20), tag `iot_list_devices_for_gateway` - [iot/src/list_gateways.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/list_gateways.php#L20), tag `iot_list_gateways` - [iot/src/list_registries.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/list_registries.php#L20), tag `iot_list_registries` - [iot/src/patch_es.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/patch_es.php#L20), tag `iot_patch_es` - [iot/src/patch_rsa.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/patch_rsa.php#L20), tag `iot_patch_rsa` - [iot/src/send_command_to_device.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/send_command_to_device.php#L20), tag `iot_send_command_to_device` - [iot/src/set_device_config.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/set_device_config.php#L20), tag `iot_set_device_config` - [iot/src/set_device_state.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/set_device_state.php#L20), tag `iot_set_device_state` - [iot/src/set_iam_policy.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/set_iam_policy.php#L20), tag `iot_set_iam_policy` - [iot/src/unbind_device_from_gateway.php:20](https://github.com/GoogleCloudPlatform/php-docs-samples/blob/2112888c5bb0754481425abe6c2bfe1017b5cc57/iot/src/unbind_device_from_gateway.php#L20), tag `iot_unbind_device_from_gateway`

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