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

android/namespace.go

@@ -366,9 +366,6 @@ type NamespaceModule struct {
 	}
 }
 
-func (n *NamespaceModule) DepsMutator(context BottomUpMutatorContext) {
-}
-
 func (n *NamespaceModule) GenerateAndroidBuildActions(ctx ModuleContext) {
 }