Revert "Re-enable pr-head"

This reverts commit 963493ae7f82b77ac340e6b9bec051565f74b83b.

Reason for revert: All jobs has been moved to the staging. the production jobs shouldn't be enabled.

Change-Id: I9229612c661428d3ee912d64d352c2e7bd2ccb8a
diff --git a/mbed-tls-pr-head.yaml b/mbed-tls-pr-head.yaml
index e56b490..479d71e 100644
--- a/mbed-tls-pr-head.yaml
+++ b/mbed-tls-pr-head.yaml
@@ -2,6 +2,7 @@
     name: mbed-tls-pr-head
     description: 'Job for testing mbed tls PR heads'
     project-type: multibranch
+    disabled: true
     prune-dead-branches: true
     days-to-keep: 60
     num-to-keep: 1000