memory_manager::gc_poll doesn't need to check is_collection_enabled

Author: qinsoon

src/memory_manager.rs

@@ -543,7 +543,7 @@ pub fn gc_poll<VM: VMBinding>(mmtk: &MMTK<VM>, tls: VMMutatorThread) {
         "gc_poll() can only be called by a mutator thread."
     );
 
-    if VM::VMCollection::is_collection_enabled() && mmtk.gc_trigger.poll(false, None) {
+    if mmtk.gc_trigger.poll(false, None) {
         debug!("Collection required");
         if !mmtk.state.is_initialized() {
             panic!("GC is not allowed here: collection is not initialized (did you call initialize_collection()?).");