Revert of Group lexical context variables for faster look up.

Revert of Group lexical context variables for faster look up. (patchset #2 id:20001 of https://codereview.chromium.org/1281883002/ )

Reason for revert:
This performance hack is no longer necessary.

Original issue's description:
> Group lexical context variables for faster look up.
>
> Currently, looking up a lexical context variable requires looking up
> the variable name and then checking its mode. This can be a bottleneck
> in Runtime_DeclareGlobals, even when no lexical context variables are
> declared.
>
> R=rossberg@chromium.org
> BUG=crbug:517778
> LOG=N
>
> Committed: https://crrev.com/a45ed17bb6aca02e940f13bbf456d660cccc86ae
> Cr-Commit-Position: refs/heads/master@{#30075}

TBR=rossberg@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=crbug:517778
Committed: https://crrev.com/3b18958be5ffed30dd3be19c2776e5bfd9fa488c
Cr-Commit-Position: refs/heads/master@{#30145}

[Yang, 2015-08-13 06:55:52]

Created Revert of Group lexical context variables for faster look up.

[commit-bot: I haz the power, 2015-08-13 06:56:03]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1290053002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1290053002/1

[commit-bot: I haz the power, 2015-08-13 06:56:35]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-13 06:56:49]

Patchset 1 (id:??) landed as
https://crrev.com/3b18958be5ffed30dd3be19c2776e5bfd9fa488c
Cr-Commit-Position: refs/heads/master@{#30145}