libui: remove frameworks/native/include/ui symlink

Remove the global include for ui. Only symlink the two
headers that are depended on by vendor code.

The changes to Region and RegionHelepr were made by the
linter. No code was changed.

Bug: 145624276
Test: Compiles

Change-Id: I1bbd99581faa703f73329ebde2da05d55950f910