workflow: remove lws 4.0.x from matrix

Author: tsl0922

.github/workflows/backend.yml

@@ -19,7 +19,7 @@ jobs:
     runs-on: ubuntu-18.04
     strategy:
       matrix:
-        lws-version: [4.1.4, 4.0.21, 3.2.3, 2.4.2]
+        lws-version: [4.1.4, 3.2.3, 2.4.2]
     steps:
       - name: Install packages
         run: |