As Ramacchandra states, the socket file is most likely owned by the root user and can safely be removed by running sudo rm /tmp/mongod-27017.sock.
One thing I notice is that in your brew services lists output it shows the user of mongodb-community as root. You should be installing and running MongoDB as your regular user. The MongoDB process should never be run as the root user unless you are directed to by MongoDB support team for troubleshooting, and even then only if you understand the implications of what happens when you run the service as the root user. This could lead to privilege escalation which could then lead to bad things happening.