Revert "tf-a-lts2.8-gerrit-tforg-l*: Set TF_GERRIT_REFSPEC to lts-v2.8 branch"

This reverts commit 90ada6da6e36723c6091518a0bbc753f7f10982c.

Reason for revert: This change should have gone to tf-a-lts2.8-tftf-gerrit-tforg-l* jobs.

Change-Id: Ib244df5bf45c941c061b64adc4f17976178a0fbd
diff --git a/tf-a-lts2.8-gerrit-tforg-l1.yaml b/tf-a-lts2.8-gerrit-tforg-l1.yaml
index 14abc93..5740048 100644
--- a/tf-a-lts2.8-gerrit-tforg-l1.yaml
+++ b/tf-a-lts2.8-gerrit-tforg-l1.yaml
@@ -34,7 +34,8 @@
             default: ''
         - string:
             name: TF_GERRIT_REFSPEC
-            default: '+refs/heads/lts-v2.8:refs/remotes/origin/lts-v2.8'
+            default: ${GERRIT_REFSPEC}
+            description: 'Parameter only used by the clone script'
         - string:
             name: TFTF_GERRIT_PROJECT
             default: 'TF-A/tf-a-tests'