Revert "[heap] Unprotect code pages on demand in MinorMC"

This reverts commit 0bf9c60c.

Reason for revert: breaks minor_mc bot

Original change's description:
> [heap] Unprotect code pages on demand in MinorMC
> 
> This reduces average pause of MinorMC in Richards benchmark from 0.32ms
> to 0.25ms:
> 
> baseline pause
>   len: 22
>   min: 0.3
>   max: 0.6
>   avg: 0.322727272727
>   [0,5[: 22
> 
> pause
>   len: 22
>   min: 0.2
>   max: 0.7
>   avg: 0.254545454545
>   [0,5[: 22
> 
> Bug: chromium:651354
> Change-Id: I701ca800d7c6986534d1de2e3051476e91a88d7d
> Reviewed-on: https://chromium-review.googlesource.com/1055507
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Reviewed-by: Hannes Payer <hpayer@chromium.org>
> Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#53125}

TBR=ulan@chromium.org,hpayer@chromium.org,mlippautz@chromium.org

Change-Id: Ib227e37fa60d608f94c3111a9b431baf0f488790
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:651354
Reviewed-on: https://chromium-review.googlesource.com/1053970Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53127}

src/heap/heap.cc

@@ -1884,6 +1884,7 @@ void Heap::MinorMarkCompact() {
   AlwaysAllocateScope always_allocate(isolate());
   IncrementalMarking::PauseBlackAllocationScope pause_black_allocation(
       incremental_marking());
+  CodeSpaceMemoryModificationScope code_modifcation(this);
   ConcurrentMarking::PauseScope pause_scope(concurrent_marking());
 
   minor_mark_compact_collector()->CollectGarbage();

src/heap/mark-compact.cc

@@ -2810,7 +2810,6 @@ class RememberedSetUpdatingItem : public UpdatingItem {
     TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("v8.gc"),
                  "RememberedSetUpdatingItem::Process");
     base::LockGuard<base::Mutex> guard(chunk_->mutex());
-    CodePageMemoryModificationScope memory_modification_scope(chunk_);
     UpdateUntypedPointers();
     UpdateTypedPointers();
   }