Remove unused TopDownMutatorContext methods

Remove methods on TopDownMutatorContext that are no longer used.
This deletes everything unique to BaseMutatorContext, so delete that
too and replace it with BaseModuleContext.

Bug: 367784740
Test: builds
Flag: EXEMPT refactor
Change-Id: Id37c7b7e3d46d75afaf7752862b08f766217f08b
diff --git a/androidmk/parser/parser_test.go b/androidmk/parser/parser_test.go
index e238f8b..21baf6b 100644
--- a/androidmk/parser/parser_test.go
+++ b/androidmk/parser/parser_test.go
@@ -142,7 +142,7 @@
 		t.Fatalf("Unexpected errors while parsing: %v", errs)
 	}
 
-	if got[0].End() < got[len(got) -1].Pos() {
-		t.Errorf("Rule's end (%d) is smaller than directive that inside of rule's start (%v)\n", got[0].End(), got[len(got) -1].Pos())
+	if got[0].End() < got[len(got)-1].Pos() {
+		t.Errorf("Rule's end (%d) is smaller than directive that inside of rule's start (%v)\n", got[0].End(), got[len(got)-1].Pos())
 	}
 }