Revert of Generate StyleBackgroundData in ComputedStyleBase. (patchset #2 id:20001 of https://codereview.chromium.org/2841433002/ )

Reason for revert:
testing

Original issue's description:
> Generate StyleBackgroundData in ComputedStyleBase.
>
> This patch generates the following fields as part of a group:
> - background ('storage_only' of type FillLayer)
> - background_color ('storage_only' of type Color)
>
> Since both fields correspond to shorthands, we specify them in
> ComputedStyleExtraFields.json5.
>
> Diff of generated files:
> https://gist.github.com/darrnshn/48a62d4ef7efe9f7a8c2b707eb57644f/revisions
>
> BUG=628043
>
> Review-Url: https://codereview.chromium.org/2841433002
> Cr-Commit-Position: refs/heads/master@{#467561}
> Committed: https://chromium.googlesource.com/chromium/src/+/9cd2845fb2b733d9d3852839d47f4dc93bdec090

TBR=nainar@chromium.org,rune@opera.com
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=628043

Review-Url: https://codereview.chromium.org/2849123002
Cr-Commit-Position: refs/heads/master@{#468557}
6 files changed