Fix coretests: Remove dependency on libnativehelper

This dependency was never needed and it makes test app
depend on private platform libraries - which is no longer allowed.

This change fixes these problems by removing dependency and renaming
JNI method.

Test: Install the test and start it.
Change-Id: I9878627148917c1b5928b98f3c86f6e6097093d6
2 files changed