AP_Scripting: fixed memory leak in sendfile()

this leaked the SocketAPM on each sendfile() call, we now rely on the
script calling close(). The net_webserver.lua is already using close()
correctly, this change just makes close able to find the socket

libraries/AP_Scripting/AP_Scripting.cpp

@@ -328,7 +328,6 @@ void AP_Scripting::thread(void) {
                 _net_sockets[i] = nullptr;
             }
         }
-        num_net_sockets = 0;
 #endif // AP_NETWORKING_ENABLED
         
         // Clear blocked commands