Build/Test Tools: Remove SpeedTrapListener.

Now that the tests can run PHPUnit cross-version and Composer will be used to install the test suite in CI, we could switch out the local copies of the [https://github.com/johnkary/phpunit-speedtrap PHPUnit speedtrap] package in favor of using the Composer package, which would prevent us having to make the WP local copies of the class compatible with later PHPUnit versions.

The SpeedTrap test listener was introduced to identify slow tests and take action on these to make them faster.

In practice, however, no notable action was ever taken based on the output of the test listener in all the years it was in place.

With that in mind, it was decided to remove the SpeedTrap test listeners without replacement.

If – at a future date – contributors would want to take action to speed up slow tests anyway, they can:
* Either add the package to their local install and use the output they receive locally to identify slow tests.
* Or use the PHPUnit native `@small` annotations in combination with the PHPUnit `PHP_Invoker` package as described in the PHPUnit documentation to [https://phpunit.readthedocs.io/en/stable/risky-tests.html#test-execution-timeout run tests with time limits].

Follow-up to [35214], [35226], [35767], [44701], [51559-51572].

Props jrf.
See #46149.
Built from https://develop.svn.wordpress.org/trunk@51573


git-svn-id: http://core.svn.wordpress.org/trunk@51184 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-alpha-51572';
+$wp_version = '5.9-alpha-51573';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.