Revert "[Memory] Speculative fix for sanitizer flakiness."

This reverts commit dc5493f4.

Reason for revert: Broke TSAN
https://build.chromium.org/p/client.v8/builders/V8%20Linux64%20TSAN/builds/18819

Original change's description:
> [Memory] Speculative fix for sanitizer flakiness.
> 
> - When allocating virtual memory, make sure addresses don't interfere
>   with hard-coded sanitizer regions.
> 
> Bug: v8:7146
> Change-Id: I5bcb664b32bf53c8581772fe329190da6033701f
> Reviewed-on: https://chromium-review.googlesource.com/833171
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Reviewed-by: Hannes Payer <hpayer@chromium.org>
> Commit-Queue: Bill Budge <bbudge@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#50208}

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

Change-Id: I8b0fcda1510854fe7fac3aba8c1a462e3350c639
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:7146
Reviewed-on: https://chromium-review.googlesource.com/834070Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50210}

src/base/platform/platform-posix.cc

@@ -206,18 +206,14 @@ size_t OS::CommitPageSize() {
 
 // static
 void* OS::GetRandomMmapAddr() {
+#if defined(ADDRESS_SANITIZER) || defined(MEMORY_SANITIZER) || \
+    defined(THREAD_SANITIZER)
+  // Dynamic tools do not support custom mmap addresses.
+  return nullptr;
+#else
   uintptr_t raw_addr;
   platform_random_number_generator.Pointer()->NextBytes(&raw_addr,
                                                         sizeof(raw_addr));
-#if defined(V8_USE_ADDRESS_SANITIZER) || defined(MEMORY_SANITIZER) || \
-    defined(THREAD_SANITIZER) || defined(LEAK_SANITIZER)
-  // If random hint addresses interfere with address ranges hard coded in
-  // sanitizers, bad things happen. This address range is copied from TSAN
-  // source but works with all tools.
-  // See crbug.com/539863.
-  raw_addr &= 0x007fffff0000ULL;
-  raw_addr += 0x7e8000000000ULL;
-#else
 #if V8_TARGET_ARCH_X64
   // Currently available CPUs have 48 bits of virtual addressing.  Truncate
   // the hint address to 46 bits to give the kernel a fighting chance of
@@ -270,9 +266,9 @@ void* OS::GetRandomMmapAddr() {
   // 10.6 and 10.7.
   raw_addr += 0x20000000;
 #endif
-#endif
 #endif
   return reinterpret_cast<void*>(raw_addr);
+#endif
 }
 
 // TODO(bbudge) Move Cygwin and Fuschia stuff into platform-specific files.