[!!!][TASK] Remove global configuration option GFX/png_to_gif

The option png_to_gif was previously used to minimize
the size of generated images. In the current web development
png (with the support of all major browsers) has overtaken gif
functionality. The option, which was off by default for some
versions, has been removed. All calls to the actual "convert"
method in GraphicalFunction have been removed, the function
itself has been marked for deprecation.

Resolves: #66906
Releases: master
Change-Id: I1e134812f55ce8026e468b12ec12ec61e4d9d104
Reviewed-on: http://review.typo3.org/39475


Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>