ScopeIterator was changed to re-parse the whole script instead of
just a single function. The CL in question went through a few
iterations. At one point, it was necessary to wrangle the source
position of generator functions  to correctly identify their
closure scope. This is no longer necessary and this CL removes
the manual source position adjustment.

Change-Id: If1a61ed32a903997b70a62cd464198f3dffa385a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1792162
Auto-Submit: Simon Zünd <szuend@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63604}