tests: Hide new private APIs

Add missing @hide
This should have been done in If04e82a13250f520d70b58991586c8ce38f0ecb1 to avoid

/opt/jenkins/android/workspace/android/cm-11.0/out/target/common/obj/PACKAGING/public_api.txt:24102:
error 4: Added public method android.test.mock.MockPackageManager.getThemedResourcesForApplication
/opt/jenkins/android/workspace/android/cm-11.0/out/target/common/obj/PACKAGING/public_api.txt:24103:
error 4: Added public method android.test.mock.MockPackageManager.getThemedResourcesForApplication

Change-Id: Ib40279065c937b130322350c1dbdf5b0b43506e3