Remove empty DepsMutator methods

Add an empty DepsMutator to ModuleBase so it doesn't have to be
implemented on every module that doesn't need it.

Test: all soong tests
Change-Id: I545a832a0dbf27386d3080377a75ea482cd9ce59

apex/key.go

@@ -19,6 +19,7 @@ import (
 	"io"
 
 	"android/soong/android"
+
 	"github.com/google/blueprint/proptools"
 )
 
@@ -61,9 +62,6 @@ func (m *apexKey) installable() bool {
 	return m.properties.Installable == nil || proptools.Bool(m.properties.Installable)
 }
 
-func (m *apexKey) DepsMutator(ctx android.BottomUpMutatorContext) {
-}
-
 func (m *apexKey) GenerateAndroidBuildActions(ctx android.ModuleContext) {
 	if ctx.Config().FlattenApex() && !ctx.Config().UnbundledBuild() {
 		// Flattened APEXes are not signed