Clean-up IssuesManager after TS migration
Clean-up IssuesManager after TS migration

Bug: chromium:1183241
Change-Id: Iff77a81884f9c511cef4abce526bd60a10c8ac26
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2744137
Reviewed-by: Wolfgang Beyer <573aa99bb19da47d816981118f95c945310dd3f4@chromium.org>
Commit-Queue: Sigurd Schneider <f04d242e109628a27a0f75fd49a87722bcf291fd@chromium.org>

ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend