Disable Azure Pipelines CI for release branch

It is completely superfluous because the release pipeline runs the exact same CI
template, and it's still really flaky.

Author: andyleejordan

.vsts-ci/azure-pipelines-ci.yml

@@ -1,11 +1,7 @@
 name: CI-$(Build.SourceBranchName)-$(Date:yyyyMMdd)$(Rev:.rr)
 
 pr: none
-
-trigger:
-  branches:
-    include:
-      - release
+trigger: none
 
 variables:
   # Don't download unneeded packages