Fix RemoveSpace memory leak.

RemoveSpace now deletes the input space. This fixes a memory leak
related to background compaction.

Change-Id: I7123297adb475b1045f7d1a42d595c53daad0faa
diff --git a/runtime/gc/heap.cc b/runtime/gc/heap.cc
index 47c13c7..bce11c7 100644
--- a/runtime/gc/heap.cc
+++ b/runtime/gc/heap.cc
@@ -472,6 +472,7 @@
     DCHECK(it != alloc_spaces_.end());
     alloc_spaces_.erase(it);
   }
+  delete space;
 }
 
 void Heap::RegisterGCAllocation(size_t bytes) {
@@ -1169,6 +1170,7 @@
       DCHECK(allocator_mem_map_.get() == nullptr);
       allocator_mem_map_.reset(main_space_->ReleaseMemMap());
       madvise(main_space_->Begin(), main_space_->Size(), MADV_DONTNEED);
+      // RemoveSpace deletes the removed space.
       RemoveSpace(main_space_);
       break;
     }