Removes a previously installed action.
This function does nothing if the action was already removed. It returns true if it was removed and false if the action wasn't found.
This does not currently return the default/previous signal handler if the last action for a
signal was just unregistered. That means that if you replaced for example
SIGTERM and then
removed the action, the program will effectively ignore
SIGTERM signals from now on, not
terminate on them as is the default action. This is OK if you remove it as part of a shutdown,
but it is not recommended to remove termination actions during the normal runtime of
application (unless the desired effect is to create something that can be terminated only by