Fix build failure

[aliXsed]

'yarn build:code' fails after not finding polkadot-dev-build-ts.js. Under node_modules/@polkadot/dev/scripts the scripts are in the "*.cjs" format according to the version of polkadot/dev that is used for this project.
If the project is solely relying on yarn build:www, then I would suggest the build script calls in package.json that are expected to fail, be removed entirely.