pcbnew: fix Duplicate assertion in legacy also (lp:1558913)

Do not assert that the item to be duplicated can be duplicated, just don't
duplicate it. The user can trigger a Duplicate on items that aren't
duplicatable, like field texts - he'll figure out that they can't be duplicated
when they aren't, no need to deliver a scary warning and risk an abort.

pcbnew/hotkeys_board_editor.cpp

@@ -1196,8 +1196,7 @@ bool PCB_EDIT_FRAME::OnHotkeyDuplicateOrArrayItem( int aIdCommand )
         break;
 
     default:
-        wxASSERT_MSG( false, wxString::Format( "Unhandled move, duplicate or array for "
-                      "object type %d", item->Type() ) );
+        evt_type = 0;
         break;
     }