Populate individual classpath_fragments' classpaths.proto configs.

To avoid duplicates on *CLASSPATH environ variables at runtime, remove
split entries from platform-*classpath, i.e. all updatable jars that
have their own classpath fragments should not appear in the
platform-*classpath's classpaths.proto config.

Bug: 180105615
Test: m && launch_cvd; atest CtsClasspathsTestCases
Change-Id: Id2759ab8e106cc183e695bf3509a6ab60ab0ef2a
Merged-In: Id2759ab8e106cc183e695bf3509a6ab60ab0ef2a