Remove DevTools test css-outline-dialog

Reason for removal: the test expects implementation details
that are no longer up-to-date. In particular, we have since
migrated to a newer version of CodeMirror.

R=tvanderlippe@chromium.org

Bug: 1203169
Change-Id: I46023d0e0f381a1160df907c803b72479ee10077
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3378351


Reviewed-by: Tim Van der Lippe <tvanderlippe@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/main@{#958032}