[heap] Remove dead code from PagedSpace

BUG=

Review URL: https://codereview.chromium.org/1909883002

Cr-Commit-Position: refs/heads/master@{#35774}

src/heap/spaces.h

@@ -2184,12 +2184,6 @@ class PagedSpace : public Space {
   static void ResetCodeStatistics(Isolate* isolate);
 #endif
 
-  // This function tries to steal size_in_bytes memory from the sweeper threads
-  // free-lists. If it does not succeed stealing enough memory, it will wait
-  // for the sweeper threads to finish sweeping.
-  // It returns true when sweeping is completed and false otherwise.
-  bool EnsureSweeperProgress(intptr_t size_in_bytes);
-
   Page* FirstPage() { return anchor_.next_page(); }
   Page* LastPage() { return anchor_.prev_page(); }