remove map file generation from build in production mode

[batzionb]

Currently map files are generated by "yarn build" for production mode as well, which increases the dist directory size and thus the container size. Since they are not used in production, I suggest to remove the configuration that generates them in production mode.

[christianvogt]

/approve I think this is a fair change. While source maps are useful for the plugin developer even in production, they can easily update this config for themselves as necessary.