Don't handle regular throw statements in `throw-error`

[JasonWeinzierl]

The rxjs-x/throw-error rule handles both the RxJS operator throwError() as well as regular throw statements. This secondary handling is unnecessary because typescript-eslint's only-throw-error rule handles the same exact functionality. Also, linting outside of RxJS code is not the job of this library. Remove lint behavior that checks regular throw statements.