Remove MutatorHandle.Parallel()

All mutators are parallel by default, remove the explicit Parallel()
calls.

Bug: 372540665
Test: all soong tests pass
Flag: EXEMPT refactor
Change-Id: I41e3a71bd13c75b7fceae91b1c4cfe678ab62df2
diff --git a/java/dexpreopt_bootjars.go b/java/dexpreopt_bootjars.go
index 5c69ff1..fa6653f 100644
--- a/java/dexpreopt_bootjars.go
+++ b/java/dexpreopt_bootjars.go
@@ -465,7 +465,7 @@
 	ctx.RegisterParallelSingletonModuleType("dex_bootjars", dexpreoptBootJarsFactory)
 	ctx.RegisterModuleType("art_boot_images", artBootImagesFactory)
 	ctx.FinalDepsMutators(func(ctx android.RegisterMutatorsContext) {
-		ctx.BottomUp("dex_bootjars_deps", DexpreoptBootJarsMutator).Parallel()
+		ctx.BottomUp("dex_bootjars_deps", DexpreoptBootJarsMutator)
 	})
 }