remove code related to tracking descriptor serving times

This had broken due to bitrot - it doesn't know about microdescriptors
at all, and afaik hasn't generally been used in ages.

changes/remove_TRACK_SERVED_TIME

@@ -0,0 +1,4 @@
+  o Removed features:
+    - Remove the ability to define TRACK_SERVED_TIME. The feature wasn't used
+      and is now outdated that microdescriptors are around.
+

src/or/dirserv.c

@@ -3482,9 +3482,6 @@ connection_dirserv_finish_spooling(dir_connection_t *conn)
 static int
 connection_dirserv_add_servers_to_outbuf(dir_connection_t *conn)
 {
-#ifdef TRACK_SERVED_TIME
-  time_t now = time(NULL);
-#endif
   int by_fp = (conn->dir_spool_src == DIR_SPOOL_SERVER_BY_FP ||
                conn->dir_spool_src == DIR_SPOOL_EXTRA_BY_FP);
   int extra = (conn->dir_spool_src == DIR_SPOOL_EXTRA_BY_FP ||
@@ -3512,9 +3509,6 @@ connection_dirserv_add_servers_to_outbuf(dir_connection_t *conn)
        * unknown bridge descriptor has shown up between then and now. */
       continue;
     }
-#ifdef TRACK_SERVED_TIME
-    sd->last_served_at = now;
-#endif
     body = signed_descriptor_get_body(sd);
     if (conn->zlib_state) {
       /* XXXX022 This 'last' business should actually happen on the last

src/or/or.h

@@ -1690,11 +1690,6 @@ typedef struct signed_descriptor_t {
    * networkstatus that listed it.  0 for "never listed in a consensus or
    * status, so far as we know." */
   time_t last_listed_as_valid_until;
-#ifdef TRACK_SERVED_TIME
-  /** The last time we served anybody this descriptor.  Used for internal
-   * testing to see whether we're holding on to descriptors too long. */
-  time_t last_served_at; /*XXXX remove if not useful. */
-#endif
   /* If true, we do not ever try to save this object in the cache. */
   unsigned int do_not_cache : 1;
   /* If true, this item is meant to represent an extrainfo. */