CP013: Remove this_thread::bind and this_thread::unbind

[AerialMantis]

Feedback from the Rapperswill meeting suggested that we should remove the this_thread::bind and this_thread::unbind interface, as it is too open to misuse and also conflicts with other more desireable approaches.

[AerialMantis]

Notes from 2018-09-03 call:

• I will add some general wording as well, explaining why this kind of interface is something we considered but didn't want to pursue.

[AerialMantis]

The MR for this has been merged, so this issue can be closed.