Changes imported from Abseil "staging" branch:

  - 3e05f2c346a9faf07088c49d590d49a9199e7edd Simplify Duration's operator-() by Jorg Brown <jorg@google.com>
  - 3c4942375a6d17e887bb6ab7cf2d0e763d58a511 Rewrite `noexcept(noexcept(allocator_type()))` to instead... by Matt Calabrese <calabrese@google.com>
  - 02f35a684201a6aa9f70e8b0a041993676f2d230 Fix comment on remove_prefix since the function is not re... by Abseil Team <absl-team@google.com>
  - ceb40aba8031e0ccec9cd49da844882df100c56f Fix mutex_test under TSAN. by Derek Mauro <dmauro@google.com>
  - 7bd12e7ddc5d074e1b9c9f037879211fa1d81f8c Slight wording tweaks for "adopting" wrappers by Abseil Team <absl-team@google.com>
  - c3580afe092e0357d40b1769314f36da1b887c65 Internal cleanup. by Greg Miller <jgm@google.com>

GitOrigin-RevId: 3e05f2c346a9faf07088c49d590d49a9199e7edd
Change-Id: If3df72fba3803398cfcbb323fb4cb84ec55511aa