removeOperator unregisted an operator by removing it from the list of
operators found at .Options$operators . All operator attributes are
that have been set will be lost.
removeOperator(x)None. Used for side-effects.
Warns if the operator has not been registered.
setOperators for registering Operators.
# Unregister ? as an operator.
if (FALSE) { # \dontrun{
removeOperator( '?' )
} # }