delete a physical instance
int delphins(ptfig, insname)
Pointer to the figure in which the instance should be deleted
Name of the instance to be deleted.
delphins delete the instance called insname in the figure
pointed to by ptfig. This instance is warrantied to be unique, because
its name is an identifier at the given hierarchical level.
The list consistency is maintainded, and the space freed.
delphins returns 1 if the instance has been deleted, 0
if no such instance exists in the list.
char *was_existing(ptfig, insname)
return delphins(ptfig, insname) ? "you just killed it!"
: "wasn't here anyway";