Changes imported from Abseil "staging" branch:

- 46a4bd582619bfc4799c1a907316e914ed0c0105 Fixes to mutex_nonprod.  Apparently this has never built.... by Greg Falcon <gfalcon@google.com>
  - 4bcf6f013aeee53057527d70100de8535aec9b93 Add some comments to copts.bzl by Tom Manshreck <shreck@google.com>
  - 54cf717b1c5dfb814721f92a8eb9df5587f5f758 Internal change by Abseil Team <absl-team@google.com>
  - d1f1c7e6e61358300963b7bd50c203740a49297d Eliminate kFast{UInt,Int}{32,64}ToBufferSize constants by Jorg Brown <jorg@google.com>

GitOrigin-RevId: 46a4bd582619bfc4799c1a907316e914ed0c0105
Change-Id: I129b6b3d27d9ae2c6eb21d6e44a52d10399ef8aa

absl/strings/internal/numbers_test_common.inc

@@ -17,16 +17,6 @@
 
 namespace {
 
-// Previously documented minimum buffer sizes for Fast*ToBuffer functions.
-// NOTE(edk): These should be deleted and uses replaced with kFastToBufferSize
-//            once existing code has been fixed to use kFastToBufferSize.
-enum {
-  kFastInt32ToBufferSize = 12,
-  kFastInt64ToBufferSize = 22,
-  kFastUInt32ToBufferSize = 12,
-  kFastUInt64ToBufferSize = 22
-};
-
 template <typename IntType>
 bool Itoa(IntType value, int base, std::string* destination) {
   destination->clear();