Remove overriden modules from deps of autogenerated filesystem modules

`android_filesystem` supports overrides, but only if the module is
overriden by another module in its deps. For AOSP CF, the autogenerated
system.img contains an additional /bin/charger. The Kati system.img does
not contain this file because it is overriden by a module which is
installed in /vendor.

This CL updates the autogen mutators to remove a module from deps if it
is overriden by another module in PRODUCT_PACKAGES or by a transitve
required module dependency of PRODUCT_PACKAGES

Test: go test ./fsgen
Test: verified that /bin/charger no longer appears in diff_test of
system for aosp_cf_x86_64
Change-Id: Idafa1db07a42519ba3c441f851480b1c6faa63b8

Change-Id: If09050a6fd110d07d975595644dba85c740027e2
diff --git a/android/module_proxy.go b/android/module_proxy.go
index 0f552dd..2a65072 100644
--- a/android/module_proxy.go
+++ b/android/module_proxy.go
@@ -205,3 +205,7 @@
 func (m ModuleProxy) DecodeMultilib(ctx ConfigContext) (string, string) {
 	panic("method is not implemented on ModuleProxy")
 }
+
+func (m ModuleProxy) Overrides() []string {
+	panic("method is not implemented on ModuleProxy")
+}