Update xcode in bots (2nd attempt)

Turns out there are 2 ways to specify an xcode version on the bots.
https://crrev.com/c/7037174 used a way that differs from the one
currently in place in the bot recipe [1]. See thread [2] for more
details. This CL reverts most xcode changes from the original CL
and adopts an approach similar to https://crrev.com/i/8594830
instead.

I would have preferred to verify this CL works ahead of landing
with led, but I don't have permission [3]. No-Try: True is added
because mac_asan is busted https://crrev.com/c/7045106.

[1] https://source.chromium.org/chromium/infra/infra_superproject/+/main:build/recipes/recipes/libyuv/libyuv.py
[2] https://chat.google.com/room/AAAAzEuhg8A/S-r4vJCVnLY
[3] https://chat.google.com/room/AAAAzEuhg8A/S-r4vJCVnLY

No-Try: True
Bug: 448679376
Change-Id: I24609c820491f5bd93052687af8989f63172b144
Reviewed-on: https://chromium-review.googlesource.com/c/libyuv/libyuv/+/7043382
Reviewed-by: Frank Barchard <fbarchard@chromium.org>
Reviewed-by: Jeremy Leconte <jleconte@google.com>
Reviewed-by: Mirko Bonadei <mbonadei@chromium.org>