[TASK] Re-work/simplify copyright header in PHP files

This patch replaces the copyright/license header in PHP files with a
new, simplified one. The new header does not show the year figure, nor
an author name, and refers to the LICENSE.txt file for the full
copyright information. License is: GPL2 or any later version.

Releases: 2.0.0
Change-Id: Iec874cd796d275d164456d48829f0306e4b86c47
Reviewed-on: https://review.typo3.org/31459
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters