[Uno-D][ProfileMenu] Remove customize profile from Guest mode

This will be tested in a followup CL where the
kExplicitBrowserSigninUIOnDesktop will be enabled by default on all
browser tests since there should be no effect with and without the
flag.

Bug: b/319397639
Change-Id: Id06647e93638888b24a77d485d9825bebc005931
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5401768


Auto-Submit: Ryan Sultanem <rsult@google.com>
Commit-Queue: David Roger <droger@chromium.org>
Reviewed-by: David Roger <droger@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1280122}