Revert "[NFC] [C++20] [Coroutines] Mention the side effect of a fix may bring regressions"

This reverts commit 6998ecd.

Author: ChuanqiXu9

clang/docs/ReleaseNotes.rst

@@ -715,9 +715,6 @@ Bug Fixes in This Version
   ``await_suspend`` could be misoptimized, including accesses to the awaiter
   object itself.
   (`#56301 <https://github.com/llvm/llvm-project/issues/56301>`_)
-  The current solution may bring performance regressions if the awaiters have
-  non-static data members. See
-  `#64945 <https://github.com/llvm/llvm-project/issues/64945>`_ for details.
 - Clang now correctly diagnoses ``function_needs_feature`` when always_inline
   callee has incompatible target features with caller.
 - Removed the linking of libraries when ``-r`` is passed to the driver on AIX.