[TASK] Remove leftover code for PHP locallang files

The PHP parser is removed, so we can drop the value from the default
list of available file extensions.

We do not need to check for the php file anymore in the
AbstractFunctionModule class.

Resolves: #78681
Releases: master
Change-Id: I25ea50c7a615374849394298a8b87e7bbf50a8d3
Reviewed-on: https://review.typo3.org/50644


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Daniel Windloff <daniel.jc.windloff@googlemail.com>
Reviewed-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Tested-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>