Revert temporary changes to pr-ci-testing

This reverts the following commits:
a838080 Add PR-850-merge to the temporary exceptions
8c51a48 Temporarily enable automatic runs of PR-906-merge

Signed-off-by: Bence Szépkúti <bence.szepkuti@arm.com>
Change-Id: Id0a08c4ca5842774b82cc499839a9833693e6f4f
diff --git a/mbed-tls-restricted-pr-ci-testing.yaml b/mbed-tls-restricted-pr-ci-testing.yaml
index 071bdfe..21f0e63 100644
--- a/mbed-tls-restricted-pr-ci-testing.yaml
+++ b/mbed-tls-restricted-pr-ci-testing.yaml
@@ -48,16 +48,8 @@
         discover-pr-origin: both
         head-filter-regex: 'PR-(758|759|850|906|916|919)-.*'
         property-strategies:
-          named-branches:
-            defaults:
-            - suppress-scm-triggering: true
-            exceptions:
-              # Temporarily enable automatic scm triggering of PR-850-merge and PR-906-merge,
-              # to test the BranchIndexingCause-specific branches modified by Mbed-TLS/mbedtls-test#71
-            - exception:
-                branch-name: 'PR-850-merge,PR-906-merge'
-                properties:
-                - suppress-scm-triggering: false
+          all-branches:
+          - suppress-scm-triggering: true
         submodule:
           disable: false
           recursive: true