system/gatekeeper: use proper nativehelper headers

libnativeheader exports headers under nativeheader. These were
available before incorrectly as global headers in order to give
access to jni.h.

Test: modules using system/gatekeeper find headers
Bug: 63762847
Change-Id: I1c238bec06b23ddff0550f3abc7670839f432b1b
3 files changed