[TASK] Remove the "@todo define visibility" in ext:rtehtmlarea

The "@todo Define visibility" is not very helpful because:

 * Nobody knows what breaks if changing the visibility
 * The code is flooded with todos which makes it hard
   to work with in an IDE

During ACME it was decided to remove the @todo again.

Resolves: #62169
Related: #61957
Releases: master
Change-Id: I891efb95449b154636604d3e70f4439bb3da832d
Reviewed-on: http://review.typo3.org/33270
Reviewed-by: Stefan Froemken <froemken@gmail.com>
Tested-by: Stefan Froemken <froemken@gmail.com>
Reviewed-by: Alexander Opitz <opitz.alexander@googlemail.com>
Tested-by: Alexander Opitz <opitz.alexander@googlemail.com>
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>