>perl -wMstrict -le
"my @dates = (
   'December 1st 2012',    'December 2nd 2012',
   'December 23rd 2012',   'December 24th 2012',
   'December 765th 2012',  'an 8th note',
   );
 ;;
 for my $date (@dates) {
   printf qq{'$date' -> };
   $date =~ s{ \d \K  (?: st | nd | rd | th) \b }{}xms;
   print qq{'$date'}
   }
"
'December 1st 2012' -> 'December 1 2012'
'December 2nd 2012' -> 'December 2 2012'
'December 23rd 2012' -> 'December 23 2012'
'December 24th 2012' -> 'December 24 2012'
'December 765th 2012' -> 'December 765 2012'
'an 8th note' -> 'an 8 note'