Revert "bsd-user: replace fprintf(stderr, ...) with error_report()"

This reverts commit 1fba5095.

That commit converted various fprintf(stderr, ...) calls to
use error_report(); however none of these bsd-user files include
a header which gives a prototype for error_report, so this
causes compiler warnings. Since these are just straightforward
reporting of command line errors, we should handle these in the
obvious way by printing to stderr, as we do for linux-user.
There's no need to drag in the error-handling framework for this,
especially since user-mode doesn't have the "maybe we need to
send this to the monitor" issues system emulation does.

Acked-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>