build: clean up proguard_flag_files

we should clean up proguard_flag_files if LOCAL_PROGUARD_ENABLED
not defined in current module in case legacy proguard_flag_files
slips into current jack_all_deps dependencies.

Test: make -j8

Change-Id: I45618fc8e821ab7a8b964fa621824209e1e9894c
Signed-off-by: ShuJie Wang <wangshujie@xiaomi.com>