Remove libtextclassifier from local shared libraries.

Move libtextclassifier from LOCAL_SHARED_LIBRARIES to
LOCAL_REQUIRED_MODULES so that it is still installed to the
system image but not linked against libandroid_runtime.  Avoids
ODR issues between libprotobuf-cpp-lite and libprotobuf-cpp-full.

Test: Checked that libtextclassifier is still built into the system image
      but not linked to libandroid_runtime.
Bug: 36350884
Change-Id: I6e57b4323a84c14e05f1b9e463ce93625d9cb3d7