- Include rsApiStubs.h instead of rs.h, and remove unused
  dependencies for rs.h in Android.mk.
  - Remove libRSDriver.so from LOCAL_REQUIRED_MODULE, since it is not
  required nor directly used by librs_jni.so.
  - Fix the discrepancy in ElementGetNativeData and
  ElementGetSubElements, respective to NDK APIs exposed in libRS.so.

  rsApiStubs.h contains all public RenderScript APIs exposed in libRS.so.
  It fixes the mismatch of the declarations and definitions of the two
  functions mentioned above. And it does not rely on the auto generated
  header (rsgApiFuncDecl.h) anymore.

Bug: 34396220
Test: mm
Change-Id: Iedb1b976cfa9033dccefe78cbe80c8022f990e53