Remove manual installation of npm when caching assets

This was only required for bootstrapping the switch to using npm. Now
the container image we use for the CI has been rebuilt and contains the
npm package.

Related ticket: https://progress.opensuse.org/issues/153427

.circleci/config.yml

@@ -170,7 +170,7 @@ jobs:
       - restore_cache: *restore_npm_cache
       - run:
           name: "Install npm dependencies"
-          command: sudo zypper -n in npm && npm install
+          command: npm install
       - save_cache: *save_npm_cache
 
   checkstyle: &test-template