Don't set up the prebuilt apk rule twice.

For apps, we don't want to set up the prebuilt apk rule twice even if
"LOCAL_MULTILIB := both", which for apps really means to set up only the
jni library rules twice. See also build/core/install_jni_libs.mk.

Change-Id: Id0406c3c605c6ede613dba06178a1710590c09b3