Remove the contextCurrency.pl set method override.

The only thing the override did was call the `update` method to force
patterns to be updated.  This is no longer needed since uddate is now
always called by the SUPER method when tokens are added.  This was
changed in openwebwork#518 and openwebwork#526.

macros/contexts/contextCurrency.pl

@@ -328,17 +328,6 @@ sub init {
 sub addToken    { }    # no tokens are needed (only uses fixed pattern)
 sub removeToken { }
 
-#
-#  Do the usual set() method, but make sure patterns are
-#  updated, since the settings may affect the currency
-#  pattern.
-#
-sub set {
-	my $self = shift;
-	$self->SUPER::set(@_);
-	$self->update;
-}
-
 #
 #  Create, set and remove extra currency symbols
 #