Disable automatic submodule handling

As of https://github.com/Mbed-TLS/mbedtls-test/pull/206 the CI scripts
handle submodules manually. Disable automatic handling which would
interfere with the proper functioning of restricted PR jobs.

Signed-off-by: Bence Szépkúti <bence.szepkuti@arm.com>
Change-Id: Id40c63e363aa35a08d6f2da9813e91cff5492978
diff --git a/mbed-tls-tf-psa-crypto-multibranch.yaml b/mbed-tls-tf-psa-crypto-multibranch.yaml
index 685c824..06fb67e 100644
--- a/mbed-tls-tf-psa-crypto-multibranch.yaml
+++ b/mbed-tls-tf-psa-crypto-multibranch.yaml
@@ -52,9 +52,6 @@
           all-branches:
           - pipeline-branch-durability-override: performance-optimized
         submodule:
-          disable: false
-          recursive: true
-          tracking: false
-          parent-credentials: true
+          disable: true
         ssh-checkout:
           credentials: mbedtls-github-ssh