[Extensions] Remove unreachable code from ExtensionInfoGenerator

After https://crrev.com/c/1861280 legacy supervised users are
deprecated, but some code about them was left in an unreachable clause.
Now this clause is removed.

Bug: 1090844

Change-Id: I3dc00348d659fc9231c6697d109dc7679da630d9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2219948
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: Oleg Davydov <burunduk@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#774723}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: e34cd04100369e71a8048b90421e780de3e4174c
1 file changed