linux-user: use libc wrapper instead of direct mremap syscall

linux-user: use libc wrapper instead of direct mremap syscall

This commit essentially reverts commit
3af72a4d98dca033492102603734cbc63cd2694a, which has replaced
five-argument calls to mremap() by direct mremap syscalls for
compatibility with glibc older than version 2.4.

The direct syscall was buggy for 64bit targets on 32bit hosts
because of the default integer type promotions. Since glibc-2.4
is now a decade old, we can remove this workaround.

Signed-off-by: Felix Janda <felix.janda@posteo.de>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>