Fix data race in propagateRROEnforcementMutator

propagateRROEnforcementMutator walks dependencies of each module and
modifies them via SetRROEnforcedForDependent.  That is unsafe in a
parallel mutator, as the same dependency could be being visited by
two parent modules at the same time.  Don't mark it as a parallel
mutator.

Test: go test -race ./...
Change-Id: I9870aaa7d165bf72b751e3ceff5a2a3eb4d74ec4
diff --git a/java/aar.go b/java/aar.go
index 7fc39b6..b162ef6 100644
--- a/java/aar.go
+++ b/java/aar.go
@@ -44,7 +44,7 @@
 	ctx.RegisterModuleType("android_library_import", AARImportFactory)
 	ctx.RegisterModuleType("android_library", AndroidLibraryFactory)
 	ctx.PostDepsMutators(func(ctx android.RegisterMutatorsContext) {
-		ctx.TopDown("propagate_rro_enforcement", propagateRROEnforcementMutator).Parallel()
+		ctx.TopDown("propagate_rro_enforcement", propagateRROEnforcementMutator)
 	})
 }