Remove ExitContextStatement.

Remove ExitContextStatement.

All the constructs that used it are now properly bracketed in the AST and we
handle abrupt exits without try/finally.  We can treat normal context exit
as occurring implicitly at the end of a body.

Committed: http://code.google.com/p/v8/source/detail?r=9189

[Kevin Millikin (Chromium), 2011-09-07 12:45:03]

We don't need this anymore.

[Steven, 2011-09-07 13:47:49]

LGTM

[fschneider, 2011-09-08 08:57:29]

LGTM as well.