send-email: do not load Data::Dumper

We never used Data::Dumper in this script.  The only reference
of it was always commented out and removed over a decade ago in
commit 4bc87a2
("send-email: Change from Mail::Sendmail to Net::SMTP")

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: Eric Wong

git-send-email.perl

@@ -22,7 +22,6 @@
 use Term::ReadLine;
 use Getopt::Long;
 use Text::ParseWords;
-use Data::Dumper;
 use Term::ANSIColor;
 use File::Temp qw/ tempdir tempfile /;
 use File::Spec::Functions qw(catfile);