Dedup prebuilt mutator registration

Test: m checkbuild
Bug: 146540677
Change-Id: I9f8a11adf61fe6f352ec1eabc7c5bac332348ba2
diff --git a/android/prebuilt_test.go b/android/prebuilt_test.go
index 600f078..8648b93 100644
--- a/android/prebuilt_test.go
+++ b/android/prebuilt_test.go
@@ -141,8 +141,7 @@
 			config := TestConfig(buildDir, nil, bp, fs)
 
 			ctx := NewTestContext()
-			ctx.PreArchMutators(RegisterPrebuiltsPreArchMutators)
-			ctx.PostDepsMutators(RegisterPrebuiltsPostDepsMutators)
+			RegisterPrebuiltMutators(ctx)
 			ctx.RegisterModuleType("filegroup", FileGroupFactory)
 			ctx.RegisterModuleType("prebuilt", newPrebuiltModule)
 			ctx.RegisterModuleType("source", newSourceModule)