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/android/prebuilt.go b/android/prebuilt.go
index 017ba76..d50841d 100644
--- a/android/prebuilt.go
+++ b/android/prebuilt.go
@@ -400,13 +400,13 @@
 }
 
 func RegisterPrebuiltsPreArchMutators(ctx RegisterMutatorsContext) {
-	ctx.BottomUp("prebuilt_rename", PrebuiltRenameMutator).Parallel().UsesRename()
+	ctx.BottomUp("prebuilt_rename", PrebuiltRenameMutator).UsesRename()
 }
 
 func RegisterPrebuiltsPostDepsMutators(ctx RegisterMutatorsContext) {
-	ctx.BottomUp("prebuilt_source", PrebuiltSourceDepsMutator).Parallel().UsesReverseDependencies()
-	ctx.BottomUp("prebuilt_select", PrebuiltSelectModuleMutator).Parallel()
-	ctx.BottomUp("prebuilt_postdeps", PrebuiltPostDepsMutator).Parallel().UsesReplaceDependencies()
+	ctx.BottomUp("prebuilt_source", PrebuiltSourceDepsMutator).UsesReverseDependencies()
+	ctx.BottomUp("prebuilt_select", PrebuiltSelectModuleMutator)
+	ctx.BottomUp("prebuilt_postdeps", PrebuiltPostDepsMutator).UsesReplaceDependencies()
 }
 
 // Returns the name of the source module corresponding to a prebuilt module