portal: drop unnecessary build steps

We'll skip adding the node_modules dir to $PATH. At the same time,
we'll no longer install ng-swagger-gen explicitly, expecting it
to be retrieved as part of the build process.

v2.10.2/portal/rockcraft.yaml

@@ -71,9 +71,6 @@ parts:
 
       export NPM_CONFIG_REGISTRY=https://registry.npmjs.org
 
-      export PATH="$PATH:$CRAFT_PART_BUILD/src/portal/node_modules/.bin"
-      npm install ng-swagger-gen
-
       npm install --unsafe-perm
       npm run generate-build-timestamp
       node --max_old_space_size=2048 \