pgsql: More trivial dead code removal: in int_to_roman(), checking for

Log Message:
-----------
More trivial dead code removal: in int_to_roman(), checking for "num == -1"
is redundant after a check has already been made for "num < 0". The "set"
variable can also be removed, as it is now no longer used. Per checking
with Karel, this is the right fix.

Per Coverity static analysis performed by EnterpriseDB.

Modified Files:
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pgsql/src/backend/utils/adt:
formatting.c (r1.88 -> r1.89)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/formatting.c.diff?r1=1.88&amp;r2=1.89)