Stop appsearch manually linking stubs

Nothing shold be depending directly on android_stub_system_current.

Stub sources and stub jars should compile against module_sdk rather
than the system sdk, so fix that. Also update some TODOs that had
incorrect instructions.

Bug: 152864915
Test: m
Change-Id: If74f258ddd32938ed485bdbb9b726e7efb2dec00
1 file changed