Add ACL rule for deleting treasuremap branches
This grants delete privileges on Treasuremap project branches to the
airship-release group.  This is required so that we can clean up the
old `v2` branch now that its contents have been moved to master, and
is no longer needed (and can be confusing).
@@ -4,6 +4,7 @@ pushMerge = group airship-release
[access "refs/heads/*"]
abandon = group treasuremap-core
create = group airship-release
+delete = group airship-release
label-Code-Review = -2..+2 group treasuremap-core
label-Verified = -1..+1 group airship-ci
label-Workflow = -1..+1 group treasuremap-core
