Revert "temp band aid fix for perf issues"

This reverts commit bd020af872330b4b198a77a3fda922b622769f1b.
SASS builder: improve minification

Use CSSMin::minify instead of Minify_CSS_Compressor::process which is up to x100 faster
Get rid of Minify_CSS_Compressor
Merge pull request #2394 from Wikia/bac-1106-improve-sass-minification

Improve SASS minification