postgres_fdw: Remove schema-qualification from cast to text.

As pointed out by Ashutosh Bapat, the header comments for this file
say that schema-qualification is needed for all and only those types
outside pg_catalog.  pg_catalog.text is not outside pg_catalog.

contrib/postgres_fdw/deparse.c

@@ -1601,7 +1601,7 @@ deparseColumnRef(StringInfo buf, int varno, int varattno, PlannerInfo *root,
 		{
 			appendStringInfoString(buf, "CASE WHEN (");
 			ADD_REL_QUALIFIER(buf, varno);
-			appendStringInfo(buf, "*)::pg_catalog.text IS NOT NULL THEN %u END", fetchval);
+			appendStringInfo(buf, "*)::text IS NOT NULL THEN %u END", fetchval);
 		}
 		else
 			appendStringInfo(buf, "%u", fetchval);
@@ -1645,7 +1645,7 @@ deparseColumnRef(StringInfo buf, int varno, int varattno, PlannerInfo *root,
 		{
 			appendStringInfoString(buf, "CASE WHEN (");
 			ADD_REL_QUALIFIER(buf, varno);
-			appendStringInfo(buf, "*)::pg_catalog.text IS NOT NULL THEN ");
+			appendStringInfo(buf, "*)::text IS NOT NULL THEN ");
 		}
 
 		appendStringInfoString(buf, "ROW(");