replace aconfig_storage_reader_java to aconfig_storage_stub

This change replace aconfig_storage_reader_jave to aconfig_storage_stub.
The former library is a normal java library, while the later is a stub
library. Since we only need to provide the symbols here, the stub
library is safer.

Test: presubmit
Change-Id: I1c098cf7ad4c0ec0d5f0b13089f04598b8f81fc3