Don't continuously rebuild mediaextractor

Use LOCAL_REQUIRED_MODULES instead of LOCAL_ADDITIONAL_DEPENDENCIES to
remove the dependency on a phony module. LOCAL_ADDITIONAL_DEPENDENCIES
also rebuilds the objects when the dependency is dirty, instead of just
making sure mediaextractor-seccomp.policy is installed.

Change-Id: I0d21d4e874b55eadaf5dfb395a85c987392250b3
diff --git a/services/mediaextractor/minijail/Android.mk b/services/mediaextractor/minijail/Android.mk
index 79182bd..17ff2c1 100644
--- a/services/mediaextractor/minijail/Android.mk
+++ b/services/mediaextractor/minijail/Android.mk
@@ -4,7 +4,7 @@
 include $(CLEAR_VARS)
 LOCAL_MODULE := mediaextractor-seccomp.policy
 LOCAL_MODULE_CLASS := ETC
-LOCAL_MODULE_PATH := $(TARGET_OUT)/etc/seccomp_policy/
+LOCAL_MODULE_PATH := $(TARGET_OUT)/etc/seccomp_policy
 
 # mediaextractor runs in 32-bit combatibility mode. For 64 bit architectures,
 # use the 32 bit policy