Fix output for references that iterate complete sets

[tsandall]

The output for references that iterate complete sets should not include the binding for the reference itself. This is already handled for partial sets. When set literals were added, we forgot to update this part of the REPL. For example:

torin:~$ opa run
OPA 0.2.1-dev (commit 6228136-dirty, built at 2016-11-10T21:14:12Z)

Run 'help' to see a list of commands.

> p[1] :- true
> p[2] :- true
> p[x]
+---+
| x |
+---+
| 1 |
| 2 |
+---+
>
>
>
> q = {1,2} :- true
> q[x]
+---+------+
| x | q[x] |
+---+------+
| 1 | true |
| 2 | true |
+---+------+