stm32/modnetwork: Remove redundant call to nimble_poll in lwip poll.

The bluetooth stack has its own dedicated polling function, see
mod_bluetooth_nimble_poll_wrapper().

ports/stm32/modnetwork.c

@@ -63,11 +63,6 @@ STATIC void pyb_lwip_poll(void) {
 
     // Run the lwIP internal updates
     sys_check_timeouts();
-
-    #if MICROPY_BLUETOOTH_NIMBLE
-    extern void nimble_poll(void);
-    nimble_poll();
-    #endif
 }
 
 void mod_network_lwip_poll_wrapper(uint32_t ticks_ms) {