ar: remove invalid extra param in bsdar_warnc calls

A number of warnings passed an exit status code to bsdar_warnc, but it
does not take exit status (as a warning, it does not exit).

MFC after: 1 week
Sponsored by: The FreeBSD Foundation

(cherry picked from commit 09319f7d3f8aefe8a6b37b1c2a6d842126a2c181)