Remove unused VR UI code

Cleans up some more VR UI code that's unused. A few notable changes:

LinearLayout::layout_length_ was only set in UTs so was 0 in production.
This means that some of it's overrides were not necessary, and were
removed.

Extensive cleanup was done to UiElement to remove methods that were
unused (i.e. not called outside UTs), including several virtual methods
with no overrides. Virtual methods with no overrides and no impl in the
base class were deleted, whereas virtual methods with no overrides but
an impl were marked as non-virtual. This included removing a bunch of
logic for HitTests, Clipping and EventHandling that were tested in UTs
but not used outside of them as well as a few setters who were either
always set to the default value or the set value was never actually
read.

Also removed ControllerModel and TextureCopyRenderer which were
fully unused, as well as cleaning up the UiElementType enum.

Finally, removed some values from ColorScheme that weren't referenced
anywhere. A future cleanup can look at taking ColorScheme away from
being an object to just being a set of static values in a namespace.

Though not yet built for Android, it looks like this should shave off
~5kb from https://crrev.com/c/5324885

Bug: 41430992
Change-Id: I55027203441c9f8fab507c991fdb2369b62439a5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5334415
Reviewed-by: Brandon Jones <bajones@chromium.org>
Auto-Submit: Alexander Cooper <alcooper@chromium.org>
Commit-Queue: Alexander Cooper <alcooper@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1276597}