deactivate-mark is a compiled Lisp function in `simple.el'.

(deactivate-mark &optional FORCE)

Deactivate the mark.
If Transient Mark mode is disabled, this function normally does
nothing; but if FORCE is non-nil, it deactivates the mark anyway.

Deactivating the mark sets `mark-active' to nil, updates the
primary selection according to `select-active-regions', and runs

If Transient Mark mode was temporarily enabled, reset the value
of the variable `transient-mark-mode'; if this causes Transient
Mark mode to be disabled, don't change `mark-active' to nil or
run `deactivate-mark-hook'.