[topology] remove unused (non const) GetExtAddress() method (#4249)
[topology] remove unused (non const) GetExtAddress() method (#4249)


librasungirl/openthread,lanyuwen/openthread,lanyuwen/openthread,jwhui/openthread,jwhui/openthread,bukepo/openthread,lanyuwen/openthread,bukepo/openthread,abtink/openthread,lanyuwen/openthread,chshu/openthread,openthread/openthread,openthread/openthread,srickardti/openthread,chshu/openthread,librasungirl/openthread,bukepo/openthread,srickardti/openthread,lanyuwen/openthread,lanyuwen/openthread,abtink/openthread,srickardti/openthread,chshu/openthread,jwhui/openthread,abtink/openthread,chshu/openthread,librasungirl/openthread,openthread/openthread,abtink/openthread,srickardti/openthread,librasungirl/openthread,jwhui/openthread,chshu/openthread,openthread/openthread,chshu/openthread,bukepo/openthread