CQ config: remove unused hide_ref_in_committed_msg.

This has been superseeded by just-in-time determination based on state
of gnumbd and git-numberer validation.

BUG=chromium:644915
R=machenbach@chromium.org,sergiyb@chromium.org
NOTRY=True

Review-Url: https://codereview.chromium.org/2583703004
Cr-Commit-Position: refs/heads/master@{#41772}

infra/config/cq.cfg

@@ -4,7 +4,6 @@
 version: 1
 cq_name: "v8"
 cq_status_url: "https://chromium-cq-status.appspot.com"
-hide_ref_in_committed_msg: true
 commit_burst_delay: 60
 max_commit_burst: 1
 target_ref: "refs/pending/heads/master"