Fix two small memory leaks in config mechanism.

The memory dangling off ssd->sesslist should be freed when ssd itself
goes away, and the font settings ctrlset we delete in gtkcfg.c should
be freed as well once it's been removed from its containing array.

Thanks to Ranjini Aravind for pointing these out.

(cherry picked from commit f4956a1f9d)

unix/gtkcfg.c

@@ -81,6 +81,7 @@ void gtk_setup_config_box(struct controlbox *b, int midsession, void *win)
             memmove(b->ctrlsets+i, b->ctrlsets+i+1,
                     (b->nctrlsets-i-1) * sizeof(*b->ctrlsets));
             b->nctrlsets--;
+            ctrl_free_set(s2);
             break;
         }
     }