patch 9.1.1622: Patch v9.1.1432 causes performance regressions

patch 9.1.1622: Patch v9.1.1432 causes performance regressions

Problem:  Patch v9.1.1432 causes performance regressions
Solution: Revert "patch 9.1.1432: GTK GUI: Buffer menu does not handle
          unicode correctly" (Yee Cheng Chin).

This reverts commit 08896dd330c6dc8324618fde482db968e6f71088.

The previous change to support Unicode characters properly in the
buffers menu resorted to removing all buffer menus and re-add the
buffers after doing a sort, per each buffer addition. This was quite
slow because if Vim is trying to load in multiple buffers at once (e.g.
when loading a session) this scales in O(n^2) and Vim can freeze for
dozens of seconds when adding a few hundred buffers.

related: #17405
related: #17928
fixes: #17897

Signed-off-by: Yee Cheng Chin <ychin.git@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>