cc bazel handlers: use better interface checking

This is a far better approach for ensuring that bazel handlers implement
the BazelHandler interface, as it causes a compile error if they do not
implement the appropriate interface methods.

Test: Manually verified no change in ninja file
Change-Id: I63a4f8b57e3aedd4c0915c2fd2eb7029e9a993aa
diff --git a/cc/library_headers.go b/cc/library_headers.go
index 6fd9568..dd2f06c 100644
--- a/cc/library_headers.go
+++ b/cc/library_headers.go
@@ -49,12 +49,12 @@
 }
 
 type libraryHeaderBazelHandler struct {
-	BazelHandler
-
 	module  *Module
 	library *libraryDecorator
 }
 
+var _ BazelHandler = (*libraryHeaderBazelHandler)(nil)
+
 func (handler *libraryHeaderBazelHandler) QueueBazelCall(ctx android.BaseModuleContext, label string) {
 	bazelCtx := ctx.Config().BazelContext
 	bazelCtx.QueueBazelRequest(label, cquery.GetCcInfo, android.GetConfigKey(ctx))