ci/lava: inherit .piglit-traces-test in .lava-piglit-traces and deduplicate configs

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36145>

.gitlab-ci/lava/gitlab-ci.yml

@@ -219,16 +219,11 @@ variables:
 
 .lava-piglit-traces:
   extends:
-    - .test-piglit
+    - .piglit-traces-test
   variables:
-    HWCI_TEST_SCRIPT: "/install/piglit/piglit-traces.sh"
     # until we overcome Infrastructure issues, give traces extra 5 min before timeout
     DEVICE_HANGING_TIMEOUT_SEC: 600
     PIGLIT_REPLAY_DEVICE_NAME: "gl-${GPU_VERSION}"
-    PIGLIT_RESULTS: "${GPU_VERSION}-replay"
-  artifacts:
-    reports:
-      junit: results/junit.xml
 
 .lava-x86_64-piglit-traces:
   extends: