[BUGFIX] config.compressCss = 1 does not work

TypoScript configuration option 'compressCss' is never tested and thus
does not work. Only the deprecated configuration option 'minifyCSS' is
taken into account.

Change-Id: Ic9d15bd1da84c92602a7e88283161c5b109d2939
Fixes: #30537
Releases: 4.6
Reviewed-on: http://review.typo3.org/5522
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer