chore(agent): cleanup agent's verbosedebug log

[lavarou]

Don't print Stack depth: ... messages. Stack depth can can be inferred from the level of indentation used in nr_php_show_exec and nr_php_show_exec_return - both use nr_php_show_exec_indentation, which uses NRPRG(php_cur_stack_depth) to calculate indentation level.

[newrelic-php-agent-bot]

Test Suite	Status	Result
Multiverse	:white_check_mark:	9/9 passing
SOAK	:white_check_mark:	56/56 passing

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 78.79%. Comparing base (d76a34b) to head (957d912). Report is 1 commits behind head on dev.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #896 +/- ## ======================================= Coverage 78.78% 78.79% ======================================= Files 193 193 Lines 27216 27214 -2 ======================================= Hits 21443 21443 + Misses 5773 5771 -2 ``` | [Flag](https://app.codecov.io/gh/newrelic/newrelic-php-agent/pull/896/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=newrelic) | Coverage Δ | | |---|---|---| | [agent-for-php-7.0](https://app.codecov.io/gh/newrelic/newrelic-php-agent/pull/896/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=newrelic) | `77.53% <ø> (ø)` | | | [agent-for-php-7.1](https://app.codecov.io/gh/newrelic/newrelic-php-agent/pull/896/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=newrelic) | `77.27% <ø> (ø)` | | | [agent-for-php-7.2](https://app.codecov.io/gh/newrelic/newrelic-php-agent/pull/896/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=newrelic) | `78.20% <ø> (ø)` | | | [agent-for-php-7.3](https://app.codecov.io/gh/newrelic/newrelic-php-agent/pull/896/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=newrelic) | `78.22% <ø> (ø)` | | | [agent-for-php-7.4](https://app.codecov.io/gh/newrelic/newrelic-php-agent/pull/896/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=newrelic) | `77.93% <ø> (ø)` | | | [agent-for-php-8.0](https://app.codecov.io/gh/newrelic/newrelic-php-agent/pull/896/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=newrelic) | `77.99% <ø> (+<0.01%)` | :arrow_up: | | [agent-for-php-8.1](https://app.codecov.io/gh/newrelic/newrelic-php-agent/pull/896/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=newrelic) | `77.98% <ø> (+<0.01%)` | :arrow_up: | | [agent-for-php-8.2](https://app.codecov.io/gh/newrelic/newrelic-php-agent/pull/896/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=newrelic) | `77.58% <ø> (+<0.01%)` | :arrow_up: | | [agent-for-php-8.3](https://app.codecov.io/gh/newrelic/newrelic-php-agent/pull/896/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=newrelic) | `77.58% <ø> (+<0.01%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=newrelic#carryforward-flags-in-the-pull-request-comment) to find out more.

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