BTW, the "multiple libraries found" message is just some helpful information provided to you by the Arduino IDE, not an error. You can ignore that message unless the library it shows having been used was not the library you intended to be used. In this case the correct library was used so all is well.
The error you should have focused on is:
Smart_Door:20: error: 'servo' does not name a type
servo.attach(2); // attaches the servo on GPIO2 to the servo object
^