Remove change to USB re DTR adding in commit 9a489ca. So I can create a stable release

Author: rogerclarkmelbourne

STM32F1/cores/maple/usb_serial.cpp

@@ -119,16 +119,9 @@ size_t n = 0;
 size_t USBSerial::write(const uint8 *buf, uint32 len)
 {
 size_t n = 0;
-
-#ifdef USB_SERIAL_REQUIRE_DTR
- if (!(bool) *this || !buf) {
-        return 0;
-    }
-#else	
-	if (!buf || !(usb_is_connected(USBLIB) && usb_is_configured(USBLIB))) {
+    if (!(bool) *this || !buf) {
         return 0;
     }
-#endif	
 
     uint32 txed = 0;
     while (txed < len) {