Delete bindings from mnesia without full table scan

mnesia:match_object/3 scans the entire table and can take many seconds
on a loaded node. This is especially bad when there are many bindings
which need to be deleted. If the object is in the table then delete it,
otherwise carry on.

Prior to this change, it was observed that there is a high % of
lock collisions in rabbit_topic_trie_binding table:

```
  lock                                 id   #tries  #collisions  collisions [%]  time [us]  duration [%] histogram [log2(us)]
 -----                                ---  ------- ------------ --------------- ---------- ------------- ---------------------
db_tab          rabbit_topic_trie_binding   258465        13627          5.2723    1389904        0.0370 |      ...XXxxXx..........     |
```

mnesia:match_object/3 uses a table index if it exists, but in the case
of rabbit_topic_trie_binding, there is no table index, so a full table
scan used to be performed.

For more context, see #1513

Partner-in-crime: @essen

Author: gerhard

src/rabbit_binding.erl

@@ -331,13 +331,8 @@ binding_action(Binding = #binding{source      = SrcName,
               Fun(Src, Dst, Binding#binding{args = SortedArgs})
       end, ErrFun).
 
-delete_object(Tab, Record, LockKind) ->
-    %% this 'guarded' delete prevents unnecessary writes to the mnesia
-    %% disk log
-    case mnesia:match_object(Tab, Record, LockKind) of
-        []  -> ok;
-        [_] -> mnesia:delete_object(Tab, Record, LockKind)
-    end.
+delete_object(Table, Record, LockKind) ->
+    mnesia:delete_object(Table, Record, LockKind).
 
 sync_route(Route, true, true, Fun) ->
     ok = Fun(rabbit_durable_route, Route, write),