Make "/*@noflip*/ /*@embed*/" annotation work

Make "/*@noflip*/ /*@embed*/" annotation work

To do it, just remove /*@noflip*/ annotations in CSSJanus after
we're done processing. They are not needed anymore and some obscure
interactions with CSSMin logic for preserving comments caused
`/*@noflip*/ /*@embed*/ background-image: url(…)` not to work
correctly (it would not be embedded).

This also requires us to always do CSSJanus processing, even when we
don't need flipping, to consistently handle the annotations.
I'm not entirely sure if this is worth it, but I still greatly prefer
doing it to documenting this stupid limitation. :)

Bug: 69698
Change-Id: I311b12b08b2dff9d45efb584db08cf4a11318f59