Fix D9 broken tests and Remove support for PHP module

Using the PHP module for Drupal sites is a security and performance risk, therefore it shouldn't be encouraged by other modules.

Step 1:
Mark the PHP snippet as deprecated in Drupal 8 for both the 2.x and 3.x versions
Remove the tests around PHP so they pass in Drupal 9.

Step 2:
Write a plugin or generate an event that easily allows users to manipulate how GA is shown on pages

We can track the progress of both steps in this issue, with step 1 getting committed with the D9 release and step 2 being done later.