Remove kAccessibilityCursorColorEnabled pref

The source of truth for cursor color enablement should be the
`kAccessibilityCursorColor` pref, so we are removing the
`kAccessibilityCursorColorEnabled` pref.

Bug: 383778297
Change-Id: Ifae0ad16a7648f45a14213873ec9cd7f8511dc7b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6094308
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Reviewed-by: Theresa Sullivan <twellington@chromium.org>
Reviewed-by: Katie Dektar <katie@chromium.org>
Commit-Queue: Jesulayomi Kupoluyi <lkupo@google.com>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1403173}