CI: Drop extra condition for sjg lab

The rules part of the template makes sure that this doesn't run until
specifically requested. Drop the check in the script itself, so it is
possible to trigger a run manually without re-pushing the tree.

Signed-off-by: Simon Glass <sjg@chromium.org>

.gitlab-ci.yml

@@ -540,9 +540,6 @@ coreboot test.py:
   dependencies: []
   tags: [ 'lab' ]
   script:
-    - if [[ -z "${SJG_LAB}" ]]; then
-        exit 0;
-      fi
     # Environment:
     #   SRC  - source tree
     #   OUT  - output directory for builds