[strong] Simplify the classes-referring-to-classes check.

[strong] Simplify the classes-referring-to-classes check.

Follow up for r28032.

We don't need to store the "corresponding outer scope class variables", it's
enough if we transmit the declaration group start to the inner class
variable.

R=rossberg@chromium.org
BUG=v8:3956
LOG=N

Review URL: https://codereview.chromium.org/1102903002

Cr-Commit-Position: refs/heads/master@{#28048}