nrfmin: remove long address support

The driver is claiming it is needed for IPv6 / 6LoWPAN support, which
is not true (the long address is never used for NRFMIN in fact) and
this assumption actually leads to an assertion when compiled as with
the `gnrc_border_router` example.

cpu/nrf5x_common/include/nrfmin.h

@@ -162,16 +162,6 @@ uint16_t nrfmin_get_addr(void);
  */
 void nrfmin_set_addr(uint16_t addr);
 
-/**
- * @brief   Get a pseudo 64-bit long address (needed by IPv6 and 6LoWPAN)
- *
- * As we do not support 64-bit addresses, we just make one up, for this we
- * simply return 4 times concatenated the 16-bit address.
- *
- * @param[out] addr     64-bit pseudo long address, as array of 4 * 16-bit
- */
-void nrfmin_get_pseudo_long_addr(uint16_t *addr);
-
 /**
  * @brief   Get the IID build from the 16-bit node address
  *

cpu/nrf5x_common/radio/nrfmin/nrfmin.c

@@ -188,13 +188,6 @@ uint16_t nrfmin_get_addr(void)
     return my_addr;
 }
 
-void nrfmin_get_pseudo_long_addr(uint16_t *addr)
-{
-    for (int i = 0; i < 4; i++) {
-        addr[i] = my_addr;
-    }
-}
-
 void nrfmin_get_iid(uint16_t *iid)
 {
     iid[0] = 0;
@@ -487,10 +480,6 @@ static int nrfmin_get(netdev_t *dev, netopt_t opt, void *val, size_t max_len)
             assert(max_len >= sizeof(uint16_t));
             *((uint16_t *)val) = NRFMIN_PAYLOAD_MAX;
             return sizeof(uint16_t);
-        case NETOPT_ADDRESS_LONG:
-            assert(max_len >= sizeof(uint64_t));
-            nrfmin_get_pseudo_long_addr((uint16_t *)val);
-            return sizeof(uint64_t);
         case NETOPT_ADDR_LEN:
             assert(max_len >= sizeof(uint16_t));
             *((uint16_t *)val) = 2;