Fixes for colorize-alpha in 2.2.0

`colorize-alpha` was present in 2.2.0 but was accidentally removed (from most occurrences) in 97fed08ef5aed29fc82620bddd578da5389e4ee5 

Also, in one case the filter list wasn't trimmed, so the second commit does this.

These commits
 * re-add `colorize-alpha` throughout
 * remove `scale-hsla` and `color-to-alpha` from `style: image-filters`