bsd-user: Remove vestiges of signal queueing code

bsd-user: Remove vestiges of signal queueing code

bsd-user was copied from linux-user at a time when it queued
signals. Remove those vestiges of thse code. Retain the init function,
even though it's now empty since other stuff will likely be added
there. Make it static since it's not called from outside of main.c

Signed-off-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>