periph/uart: removed UART_NUMOF check

drivers/include/periph/uart.h

@@ -57,15 +57,6 @@
 extern "C" {
 #endif
 
-/**
- * @brief   Make sure the number of available UART devices is defined
- * @{
- */
-#ifndef UART_NUMOF
-#error "UART_NUMOF undefined for the target platform"
-#endif
-/** @} */
-
 /**
  * @brief   Define default UART type identifier
  * @{