ci/build: Do not do LTO on any pre-merge job

Running LTO on pre-merge can be time-consuming,
especially on (over)loaded CI.

Let's keep it in nightly jobs to ensure coverage without causing
timeouts in pre-merge pipelines.

Signed-off-by: David Heidelberg <david@ixit.cz>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31790>

.gitlab-ci/meson/build.sh

@@ -117,12 +117,7 @@ case $CI_PIPELINE_SOURCE in
       fi
       ;;
     *)
-      # run Fedora with LTO in pre-merge for now
-      if [ "$CI_JOB_NAME" == "fedora-release" ]; then
-	      LTO=true
-      else
-	      LTO=false
-      fi
+      LTO=false
       ;;
 esac