Certain identifiers are treated as infix operators with a given precedence and
associativity (left or right). The call unparse_as_infix "op" removes op
from the list of infix identifiers, if it was indeed there.
FAILURE CONDITIONS
Never fails, even if the given string did not originally have infix status.
COMMENTS
Take care with applying this to some of the built-in operators, or parsing may
fail in existing libraries.