Remove google_analytics_counter.api.php as the code and hooks in it are no longer used

Problem/Motivation

This a leftover code from the Drupal 7 version. Instead of those old hooks we now have google_analytics_counter.query_alter event, custom GoogleAnalyticsCounterResultProcessor plugin, and overridable google_analytics_counter.cron service to extend the module functionality with custom code. This should be documented soon in #3368166: Update module documentation about 4.0.0 usage and new features.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes