Remove substrate-ui.parity.io from CORS whitelist (#5142)

The only up-to-date deployment of PolkadotJS apps is currently on https://polkadot.js.org/apps/.
https://substrate-ui.parity.io is only useful as deliberately kept outdated version of Apps, to be used for projects still on Substrate 1.0
It cannot be used with the up-to-date chains running the Substrate 2.0 codebase, and probably won't be maintained much longer.