Remove now-unnecessary dbghelp.dll suitable for XP

I added this in
https://bugs.chromium.org/p/chromium/issues/detail?id=460506. I believe
it to be unnecessary now. This is not a shipped DLL, it's only in the
output dir for bots.

R=mark@chromium.org
BUG=579196

Review URL: https://codereview.chromium.org/1857413002

Cr-Commit-Position: refs/heads/master@{#385356}
5 files changed