Revert "linux: Raise an error if configuring a pullup when that is not supported"

This reverts commit 70ea0806d96df5a8ea83793da46f2676d9695e69.

The above commit breaks software spi on linux hosts.  Revert that
commit until an improved error check can be implemented.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/linux/gpio.c

@@ -153,9 +153,6 @@ gpio_in_reset(struct gpio_in g, int8_t pull_up)
     } else if (pull_up < 0) {
         req.flags |= GPIOD_LINE_REQUEST_FLAG_BIAS_PULL_DOWN;
     }
-#else
-    if (pull_up)
-        shutdown("Linux gpio interface does not support pullup/pulldown");
 #endif
     req.lineoffsets[0] = g.line->offset;
     strncpy(req.consumer_label, GPIO_CONSUMER, sizeof(req.consumer_label) - 1);