Blender Git Loki

UI: Remove old hacks for dynamic scrollbar hiding

Although we still dynamically hide scrollbars, they don't change the
region size anymore. They are simply drawn on top of the region content.
Because of this, some hacks introduced by fa28e50ac2a7 are no longer
necessary.
Without these hacks, the scrollbar visibility is evaluated much more
often (cheap operation) which should be more reliable and possibly solve
some glitches.

Also replaces integers passed as booleans.

Fixes T75782.