Revert r257779: "MemorySanitizer: adjust stack size to work around an MSan bug."

The bug has long been fixed so can remove this workaround.

BUG=353687
TBR=thakis@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/536903003

Cr-Commit-Position: refs/heads/master@{#293145}

base/threading/platform_thread_linux.cc

@@ -107,12 +107,11 @@ void InitOnThread() {}
 void TerminateOnThread() {}
 
 size_t GetDefaultThreadStackSize(const pthread_attr_t& attributes) {
-#if !defined(THREAD_SANITIZER) && !defined(MEMORY_SANITIZER)
+#if !defined(THREAD_SANITIZER)
   return 0;
 #else
   // ThreadSanitizer bloats the stack heavily. Evidence has been that the
   // default stack size isn't enough for some browser tests.
-  // MemorySanitizer needs this as a temporary fix for http://crbug.com/353687
   return 2 * (1 << 23);  // 2 times 8192K (the default stack size on Linux).
 #endif
 }