bsd-user/mmap.c: MAP_ symbols are defined, so no need for ifdefs

bsd-user/mmap.c: MAP_ symbols are defined, so no need for ifdefs

All these MAP_ symbols are always defined on supported FreeBSD versions
(12.2 and newer), so remove the #ifdefs since they aren't needed.

Signed-off-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Acked-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Kyle Evans <kevans@FreeBSD.org>