Remove some superfluous //ui/gfx includes from //content headers

With the exception of ui/gfx/color_utils.h, code in //ui/gfx use
namespace gfx, so if "gfx::" does not appear in a header, then it does
not need the //ui/gfx includes. The command below generated the list of
edited files:

git grep -l '^#include "ui/gfx' content|grep '\.h$'|xargs grep -L gfx::

Clean up those headers and then do IWYU to fix the build.

Bug: 40318405
Change-Id: Ic16e4595ee22e4afbf4fb4da469b234a2f82d9c4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6558729
Reviewed-by: Rakina Zata Amni <rakina@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1462261}