chore: remove unused templates in java_library

[JoeWang1127]

In this PR:

• Remove template files in samples/ directory in java library.

[snippet-bot[bot]]

Here is the summary of changes.

You are about to delete 1 region tag.

- [synthtool/gcp/templates/java_library/samples/install-without-bom/pom.xml:30](https://github.com/googleapis/synthtool/blob/6612ab8f3afcd5e292aecd647f0fa68812c9f5b5/synthtool/gcp/templates/java_library/samples/install-without-bom/pom.xml#L30), tag `{{metadata['repo'`

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[suztomo]

I see it's used https://github.com/googleapis/java-bigtable/blob/main/samples/install-without-bom/pom.xml