Revert "logmsg_reencode(): warn when iconv() fails"

Revert "logmsg_reencode(): warn when iconv() fails"

This reverts commit fd680bc5 (logmsg_reencode(): warn when iconv()
fails, 2021-08-27).  Throwing a warning for each and every commit
that gets reencoded, without allowing a way to squelch, would make
it unpleasant for folks who have to deal with an ancient part of the
history in an old project that used wrong encoding in the commits.