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/bootclasspath.go b/java/bootclasspath.go
index 029f6f6..3413cf3 100644
--- a/java/bootclasspath.go
+++ b/java/bootclasspath.go
@@ -29,7 +29,7 @@
 
 func registerBootclasspathBuildComponents(ctx android.RegistrationContext) {
 	ctx.FinalDepsMutators(func(ctx android.RegisterMutatorsContext) {
-		ctx.BottomUp("bootclasspath_deps", bootclasspathDepsMutator).Parallel()
+		ctx.BottomUp("bootclasspath_deps", bootclasspathDepsMutator)
 	})
 }