Modularize chrome/browser/profiles unit tests

Move profile_avatar_icon_util_unittest.cc and
profile_destroyer_unittest.cc from //chrome/test into the existing
source_set("unit_tests") in //chrome/browser/profiles (guarded
!is_android to match their prior placement). //chrome/test already
depends on //chrome/browser/profiles:unit_tests.

Bug: None
Change-Id: I30c323fdcde25a7b9f4df44963b21ce15c244680
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/8067096
Commit-Queue: Erik Chen <erikchen@chromium.org>
Reviewed-by: Thomas Lukaszewicz <tluk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1659573}