Here is one way:

#! perl
use Modern::Perl;

my $a = "December 14th 2012";
my $b = "December 21st 2012";
my $c = "December 22nd 2012";

for ($a, $b, $c)
{
    my @fields = split;
    $fields[1] =~ s/st|nd|rd|th//;
    $_ = join(' ', @fields);
    say;
}
[download]

Output:

12:58 >perl 433_SoPW.pl
December 14 2012
December 21 2012
December 22 2012

12:58 >
[download]

Hope that helps,