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)