Drop the $GITP4 variable that was used to specify the script in
contrib/fast-import/. The command is called "git p4" now, not
"git-p4".
Note that configuration variables will remain in a section called
"git-p4".
Signed-off-by: Pete Wyckoff <pw@padd.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>