[TASK] Change APC cache preset condition

This commit removes the check for minimum total apc cache size.
It should be enough to check for at least 5 MB free memory.

Change-Id: Ia8f6d2aaf9030c303534f7c27f2c73479aa4632a
Resolves: #71802
Releases: master, 7.6
Reviewed-on: https://review.typo3.org/44929


Reviewed-by: Alexander Opitz <opitz.alexander@googlemail.com>
Tested-by: Alexander Opitz <opitz.alexander@googlemail.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>