Correct way to remove a red wire from a circuit
Cap each end with a wire nut and leave it in its junction box. 

Do not trim away the ends of the wires. That could confuse a future maintainer, and someone might find a use for that wire someday. 

If you maintain infrastructure documentation on your home, add a note describing the abandoned wire. 

If you do not maintain infrastructure documentation on your home, start now. Begin with a note describing the abandoned wire.