oslib-posix: Remove OpenBSD workaround for fcntl("/dev/null", F_SETFL, O_NONBLOCK) failure

OpenBSD prior to 6.3 required a workaround to utilize fcntl(F_SETFL) on memory
devices.

Since modern verions of OpenBSD that are only officialy supported and buildable
on do not have this issue I am garbage collecting this workaround.

Signed-off-by: Brad Smith <brad@comstyle.com>

Message-Id: <YGYECGXQhdamEJgC@humpty.home.comstyle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

util/oslib-posix.c

@@ -273,17 +273,6 @@ int qemu_try_set_nonblock(int fd)
         return -errno;
     }
     if (fcntl(fd, F_SETFL, f | O_NONBLOCK) == -1) {
-#ifdef __OpenBSD__
-        /*
-         * Previous to OpenBSD 6.3, fcntl(F_SETFL) is not permitted on
-         * memory devices and sets errno to ENODEV.
-         * It's OK if we fail to set O_NONBLOCK on devices like /dev/null,
-         * because they will never block anyway.
-         */
-        if (errno == ENODEV) {
-            return 0;
-        }
-#endif
         return -errno;
     }
     return 0;