infra config: Remove "WebKit Mac Builder (dbg)" from scheduler.

It was removed before, but I didn't cleanup one line.

TBR=vadimsh@chromium.org

No-Try: True
Change-Id: I84fe015052ea7a679d38e37d41b61ac64e8f4089
Reviewed-on: https://chromium-review.googlesource.com/994379
Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547865}

infra/config/global/luci-scheduler.cfg

@@ -100,7 +100,6 @@ trigger {
   triggers: "Mac Builder"
   triggers: "Mac Builder (dbg)"
   triggers: "Mac FYI GPU ASAN Release"
-  triggers: "WebKit Mac Builder (dbg)"
 
   # Windows. Sorted alphabetically.
   triggers: "GPU FYI Win Builder"