examples/nimble: fix example after update to latest master

this example is broken since bc68d95

since apache/mynewt-nimble@bf76183
ble_hci_sock_init is called from nimble code, so we can't call it again in example code

examples/nimble/nimble_main.c

@@ -68,7 +68,6 @@
  ****************************************************************************/
 
 void ble_hci_sock_ack_handler(FAR void *param);
-void ble_hci_sock_init(void);
 void ble_hci_sock_set_device(int dev);
 
 /****************************************************************************
@@ -270,7 +269,6 @@ int main(int argc, FAR char *argv[])
 #endif
 
   nimble_port_init();
-  ble_hci_sock_init();
 
   /* Initialize services */