ctfdump: Use getprogname()
Also remove no longer used function getpname().
Reviewed by: markj
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D38740
(cherry picked from commit 3dd5524264095ed8612c28908e13f80668eff2f9)
(cherry picked from commit 994eb2fb8a901c883f2bd24fa29c6cd513cb4340)