Revert of [parser] Refactor of Parse*Statement*, part 1 (patchset #2 id:20001 of https://codereview.chromium.org/2307073002/ )

Reason for revert:
https://build.chromium.org/p/client.v8.ports/builders/V8%20Mips%20-%20builder

Original issue's description:
> [parser] Refactor of Parse*Statement*, part 1
>
> This patch moves the following parsing methods to ParserBase:
>
> - ParseStatementList
> - ParseStatementListItem
> - ParseStatement
> - ParseSubStatement (subsumed in ParseStatement)
> - ParseStatementAsUnlabeled
>
> It also refactors the Target and TargetScope objects, used by the
> parser.
>
> R=adamk@chromium.org, marja@chromium.org
> BUG=
> LOG=N
>
> Committed: https://crrev.com/df29f3fda25660075a273cc27ad9f7787f321072
> Cr-Commit-Position: refs/heads/master@{#39167}

TBR=adamk@chromium.org,marja@chromium.org,nikolaos@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review-Url: https://codereview.chromium.org/2313703002
Cr-Commit-Position: refs/heads/master@{#39169}