Restore consistency between .mailmap and AUTHORS

The lists are to be sorted line by line, which is easier to do than
sorting based on an arbitrarily-positioned substring within each
line.

Change-Id: Ie5e6552e2468545a5800c4bc145cc2b4da1ed4a0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2982601
Auto-Submit: Mathias Bynens <mathias@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75353}

.mailmap

@@ -8,7 +8,7 @@
 #
 # See https://git-scm.com/docs/gitmailmap for more information.
 #
-# Please keep the list sorted by the new email address.
-#
+# Please keep the list sorted.
+
 Clemens Backes <clemensb@chromium.org> Clemens Hammacher <clemensh@chromium.org>
 Timothy Gu <timothygu@chromium.org> <timothygu99@gmail.com>