Revert^2 "Define FeatureFlagsService."

This revert contains one small fix: The prior change included
changes in core/java/Android.bp and a corresponding line in
services/flags/Android.bp that causes problems in
StrictJavaPackagesTest
#testBootClasspathAndSystemServerClasspath_nonDuplicateClasses

Specifically resulting in this bug being filed: http://b/290929382


de960774

Bug: 279054964
Change-Id: Ia2ac95bb22144ff8be84c711604db72d039a814d