makefs: Remove impossible if condition

This test is inside the else block for if (*oldname == '.'), so
*oldname cannot be '.' here.

Reviewed by: kevans
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D48243

(cherry picked from commit 788e1eb7c199297aa438fc5cb6caabc9be01b419)