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