Make system_server stubs consistent with other stubs

Include the module_api stubs in system_server one instead of
putting both of these jars on the classpath. Also rename it
to be in line with the other stubs.

Bug: 149293194
Test: m
Exempt-From-Owner-Approval: approved internally
Change-Id: Iead5af4152a49cd59a4fd7afc0312c2f0c872c1e
Merged-In: Iead5af4152a49cd59a4fd7afc0312c2f0c872c1e
(cherry picked from commit bbd78556)