gitlab-ci: Remove LAB_ONLY variable

We don't actually need the LAB_ONLY variable, since we can control which
stages run using the other variables (TEST_SUITES, TEST_PY, WORLD_BUILD).

To run only lab jobs, we can set TEST_PY, WORLD_BUILD and TEST_SUITES to
"0". The only advantage to LAB_ONLY is that it avoids doing this. But we
can create a script to handle it.

So drop this special variable.

Signed-off-by: Simon Glass <simon.glass@canonical.com>

.gitlab-ci.yml

@@ -10,7 +10,6 @@ variables:
   TEST_PY: "1"
   TEST_SPEC: ""
   WORLD_BUILD: "1"
-  LAB_ONLY: ""
   SJG_LAB: ""
   PLATFORM: linux/amd64,linux/arm64
   GIT_CLONE_PATH: $CI_BUILDS_DIR/$CI_RUNNER_ID/$CI_CONCURRENT_ID/u-boot
@@ -42,8 +41,6 @@ stages:
   #   - privileged = true in /etc/gitlab-runner/config.toml
   #   OR passwordless sudo for: modprobe, cryptsetup, dd
   rules:
-    - if: $LAB_ONLY == "1"
-      when: never
     - if: $TEST_PY == "1"
       when: always
     - if: $TEST_PY == $CI_JOB_NAME
@@ -145,8 +142,6 @@ stages:
 .world_build:
   stage: world_build
   rules:
-    - if: $LAB_ONLY == "1"
-      when: never
     - if: $WORLD_BUILD == "1"
       when: always
     - when: never
@@ -229,8 +224,6 @@ build all other platforms:
 .test_suites:
   stage: test_suites
   rules:
-    - if: $LAB_ONLY == "1"
-      when: never
     - if: $TEST_SUITES == "1"
       when: always
     - when: never
@@ -376,8 +369,6 @@ Examples:
 .python_check_template:
   stage: test.py
   rules:
-    - if: $LAB_ONLY == "1"
-      when: never
     - if: $TEST_PY == "1"
       when: always
     - if: $TEST_PY == $CI_JOB_NAME