Remove include/private/android_filesystem_capability.h

android_filesystem_capability.h should be included as part of
libcutils, not as a global include.  It looks like the few users of
this file already do this correctly, so it's time to remove the
symlink.

Test: treehugger
Change-Id: I150dc5fee24bef3518b1f26728ef2bec669ee63a