Change from boost mutex to standard mutex locks in fetch_teleop

[cjds]

Because locks are standard now?

https://github.com/fetchrobotics/fetch_ros/blob/melodic-devel/fetch_teleop/src/joystick_teleop.cpp#L153

https://en.cppreference.com/w/cpp/thread/mutex

[moriarty]

:+1:

[moriarty]

Can also change boost::shared_ptr to std::shared_ptr.