https://cs.chromium.org/chromium/src/third_party/WebKit/Source/modules/mediastream/NavigatorUserMediaError.idl has [NoInterfaceObject], so removing that would be very low risk.

It's not just a rename though, MediaStreamError is a typedef, and the main change would be in changing NavigatorUserMediaErrorCallback from a callback interface to a callback function. Together with that it would make good sense to update the argument type to the callback and remove NavigatorUserMediaError which would become unused.

https://w3c.github.io/mediacapture-main/#navigatorusermediaerrorcallback is the new spec.