teensy-3.x:Removed call to khci_usbattach

The call is not need by the driver if CONFIG_USBDEV_BUSPOWERED=y
  The class register will enable the soft connect pull up. The
  khci_usbattach call only set a flag, and that  flag is only tested
  in the class register. On a USB powered device if we are running we
  are attached.

configs/teensy-3.x/src/k20_appinit.c

@@ -80,14 +80,6 @@ int board_app_initialize(uintptr_t arg)
 {
   int ret;
 
-#ifdef CONFIG_USBDEV
-  /* Teensy is powered from usb and (bug?) only boots from being programmed, 
-   * so if usb is compiled in signal the controller driver that we're attached now.
-   */
-
-  khci_usbattach();
-#endif
-
 #ifdef CONFIG_PWM
   /* Initialize PWM and register the PWM device. */