[heap] Remove unused methods in SemiSpace.

Change-Id: I6146f5e566884b1d24ecb9ee6f154ad581ef2b66
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2560722
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71414}

src/heap/new-spaces.h

@@ -74,8 +74,6 @@ class SemiSpace : public Space {
 
   bool EnsureCurrentCapacity();
 
-  Address space_end() { return memory_chunk_list_.back()->area_end(); }
-
   // Returns the start address of the first page of the space.
   Address space_start() {
     DCHECK_NE(memory_chunk_list_.front(), nullptr);
@@ -147,9 +145,6 @@ class SemiSpace : public Space {
   const Page* first_page() const {
     return reinterpret_cast<const Page*>(Space::first_page());
   }
-  const Page* last_page() const {
-    return reinterpret_cast<const Page*>(Space::last_page());
-  }
 
   iterator begin() { return iterator(first_page()); }
   iterator end() { return iterator(nullptr); }