[clang-tidy][docs] Remove the entry about 'cppcoreguidelines-init-variables' from the release notes

The patch in http://reviews.llvm.org/D106431 landed in commit
4a097ef to the main branch.
However, this patch was also backported to upcoming release 13.0.0 in
commit 8dcdfc0, which makes this entry
in the release notes **NOT** a new thing for the purposes of 14.0.0.

Author: whisperity

clang-tools-extra/docs/ReleaseNotes.rst

@@ -78,12 +78,6 @@ New check aliases
 Changes in existing checks
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-- Improved :doc:`cppcoreguidelines-init-variables<clang-tidy/checks/cppcoreguidelines-init-variables>` check.
-
-  Removed generating fixes for enums because the code generated was broken, trying to initialize the enum from an integer.
-
-  The check now also warns for uninitialized scoped enums.
-
 Removed checks
 ^^^^^^^^^^^^^^