[cleanup] Remove InitializationMode and use STATIC_ASSERT in spaces.h

Bug: v8:9183
Change-Id: Ibdf4633a9a57d0a37e1e2ef8930471e6acbf7e13
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1621944Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Maciej Goszczycki <goszczycki@google.com>
Cr-Commit-Position: refs/heads/master@{#61698}

src/heap/spaces.h

@@ -816,8 +816,7 @@ class MemoryChunk {
   friend class PagedSpace;
 };
 
-static_assert(sizeof(std::atomic<intptr_t>) == kSystemPointerSize,
-              "sizeof(std::atomic<intptr_t>) == kSystemPointerSize");
+STATIC_ASSERT(sizeof(std::atomic<intptr_t>) == kSystemPointerSize);
 
 // -----------------------------------------------------------------------------
 // A page is a memory chunk of a size 512K. Large object pages may be larger.
@@ -943,8 +942,6 @@ class Page : public MemoryChunk {
 #endif  // DEBUG
 
  private:
-  enum InitializationMode { kFreeMemory, kDoNotFreeMemory };
-
   friend class MemoryAllocator;
 };