chore(agent): remove obsolete PHP 7.0/7.1 ZEND_MODULE_API_NO usage

[hahuja2]

This PR removes obsolete PHP 7.0/7.1 ZEND_MODULE_API_NO usage from the agent codebase.

[newrelic-php-agent-bot]

Test Suite	Status	Result
Multiverse	❌	5/8 passing
SOAK	❌	83/85 passing

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 42.85714% with 4 lines in your changes missing coverage. Please review.

Please upload report for BASE (remove-obsolete-code@a333a7d). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
agent/php_call.c	33.33%	4 Missing ⚠️

Additional details and impacted files

@@                   Coverage Diff                   @@
##             remove-obsolete-code    #1092   +/-   ##
=======================================================
  Coverage                        ?   78.91%           
=======================================================
  Files                           ?      191           
  Lines                           ?    26887           
  Branches                        ?        0           
=======================================================
  Hits                            ?    21219           
  Misses                          ?     5668           
  Partials                        ?        0           

Flag	Coverage Δ
agent-for-php-7.3	78.47% <42.85%> (?)
agent-for-php-7.4	78.33% <42.85%> (?)

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