[ci] Remove null safety experiment flag (#24392)

diff --git a/.cirrus.yml b/.cirrus.yml
index c56db8d..103cf80 100644
--- a/.cirrus.yml
+++ b/.cirrus.yml
@@ -55,7 +55,7 @@
         bin/flutter analyze --dartdocs --flutter-repo --local-engine=host_debug_unopt
       test_framework_script: |
         cd $FRAMEWORK_PATH/flutter/packages/flutter
-        ../../bin/flutter test --local-engine=host_debug_unopt --null-assertions --sound-null-safety --enable-experiment=non-nullable
+        ../../bin/flutter test --local-engine=host_debug_unopt --null-assertions --sound-null-safety
     # TODO(fujino): remove this once ci/licenses.sh is run on LUCI
     - name: licenses_check
       build_script: |
diff --git a/ci/analyze.sh b/ci/analyze.sh
index 85c2c23..832b479 100755
--- a/ci/analyze.sh
+++ b/ci/analyze.sh
@@ -62,7 +62,6 @@
 autoninja -C "$SRC_DIR/out/host_debug_unopt" generate_dart_ui
 analyze \
   --options "$FLUTTER_DIR/analysis_options.yaml" \
-  --enable-experiment=non-nullable \
   "$SRC_DIR/out/host_debug_unopt/gen/sky/bindings/dart_ui/ui.dart"
 
 echo "Analyzing flutter_frontend_server..."