delete refs/pfq/ space

This was used by the old CrOS PFQ builders, but those are no more after
the migration to the Chromium CQ.

Change-Id: I481319f5b00770ba31ab0b918383a2dfc173bddc
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/+/5332275
Reviewed-by: Sergey Frolov <sfrolov@google.com>
2 files changed