[heap] Remove unused CompactionMode flag

src/heap/incremental-marking.cc

Index: src/heap/incremental-marking.cc
diff --git a/src/heap/incremental-marking.cc b/src/heap/incremental-marking.cc
index a05c0c1e4ff6e892972b6fc3a3f9f61e18ac38e2..05beb5f841623c93869f47cf6069bfa187b83a9a 100644
--- a/src/heap/incremental-marking.cc
+++ b/src/heap/incremental-marking.cc
@@ -519,9 +519,8 @@ void IncrementalMarking::StartMarking() {
         "[IncrementalMarking] Start marking\n");
   }
 
-  is_compacting_ = !FLAG_never_compact &&
-                   heap_->mark_compact_collector()->StartCompaction(
-                       MarkCompactCollector::INCREMENTAL_COMPACTION);
+  is_compacting_ =
+      !FLAG_never_compact && heap_->mark_compact_collector()->StartCompaction();
 
   state_ = MARKING;