linux-user: Clean up unused header

Clean up unused (already commented-out) header from syscall.c.

Signed-off-by: Gustavo Romero <gustavo.romero@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

linux-user/syscall.c

@@ -54,7 +54,6 @@
 #include <utime.h>
 #include <sys/sysinfo.h>
 #include <sys/signalfd.h>
-//#include <sys/user.h>
 #include <netinet/in.h>
 #include <netinet/ip.h>
 #include <netinet/tcp.h>