Remove variables; fix gcc 4.7 warnings

My GCC warns when variables are assigned to but never used.  There
were a few like that in the 6816/6465 branches.

src/or/channel.c

@@ -552,7 +552,7 @@ channel_add_to_digest_map(channel_t *chan)
 static void
 channel_remove_from_digest_map(channel_t *chan)
 {
-  channel_t *tmp, *head;
+  channel_t *tmp;
 
   tor_assert(chan);
 
@@ -588,7 +588,6 @@ channel_remove_from_digest_map(channel_t *chan)
   tmp = digestmap_get(channel_identity_map, chan->identity_digest);
   if (tmp) {
     /* Okay, it's here */
-    head = tmp; /* Keep track of list head */
     /* Look for this channel */
     while (tmp && tmp != chan) {
       tmp = tmp->next_with_same_id;

src/or/channeltls.c

@@ -917,7 +917,6 @@ void
 channel_tls_handle_var_cell(var_cell_t *var_cell, or_connection_t *conn)
 {
   channel_tls_t *chan;
-  int handshaking;
 
 #ifdef KEEP_TIMING_STATS
   /* how many of each cell have we seen so far this second? needs better
@@ -953,8 +952,6 @@ channel_tls_handle_var_cell(var_cell_t *var_cell, or_connection_t *conn)
     return;
   }
 
-  handshaking = (TO_CONN(conn)->state != OR_CONN_STATE_OPEN);
-
   if (TO_CONN(conn)->marked_for_close)
     return;
 

src/or/circuitlist.c

@@ -100,18 +100,16 @@ circuit_set_circid_chan_helper(circuit_t *circ, int direction,
   chan_circid_circuit_map_t *found;
   channel_t *old_chan, **chan_ptr;
   circid_t old_id, *circid_ptr;
-  int was_active, make_active, attached = 0;
+  int make_active, attached = 0;
 
   if (direction == CELL_DIRECTION_OUT) {
     chan_ptr = &circ->n_chan;
     circid_ptr = &circ->n_circ_id;
-    was_active = circ->next_active_on_n_chan != NULL;
     make_active = circ->n_chan_cells.n > 0;
   } else {
     or_circuit_t *c = TO_OR_CIRCUIT(circ);
     chan_ptr = &c->p_chan;
     circid_ptr = &c->p_circ_id;
-    was_active = c->next_active_on_p_chan != NULL;
     make_active = c->p_chan_cells.n > 0;
   }
   old_chan = *chan_ptr;

src/or/circuitmux_ewma.c

@@ -265,7 +265,6 @@ ewma_alloc_circ_data(circuitmux_t *cmux,
                      cell_direction_t direction,
                      unsigned int cell_count)
 {
-  ewma_policy_data_t *pol = NULL;
   ewma_policy_circ_data_t *cdata = NULL;
 
   tor_assert(cmux);
@@ -276,8 +275,6 @@ ewma_alloc_circ_data(circuitmux_t *cmux,
   /* Shut the compiler up */
   tor_assert(cell_count == cell_count);
 
-  pol = TO_EWMA_POL_DATA(pol_data);
-
   cdata = tor_malloc_zero(sizeof(*cdata));
   cdata->_base.magic = EWMA_POL_CIRC_DATA_MAGIC;
   cdata->circ = circ;
@@ -309,13 +306,11 @@ ewma_free_circ_data(circuitmux_t *cmux,
                     circuitmux_policy_circ_data_t *pol_circ_data)
 
 {
-  ewma_policy_data_t *pol = NULL;
   ewma_policy_circ_data_t *cdata = NULL;
 
   tor_assert(cmux);
   tor_assert(circ);
   tor_assert(pol_data);
-  pol = TO_EWMA_POL_DATA(pol_data);
 
   if (!pol_circ_data) return;