Remove variable shadowing

Commit a2e35b53 should have removed the variable declaration in the
inner block, but didn't.  As a result, the returned address might end up
not being what was intended.

src/backend/commands/alter.c

@@ -446,7 +446,6 @@ ExecAlterObjectSchemaStmt(AlterObjectSchemaStmt *stmt,
 				Relation	relation;
 				Oid			classId;
 				Oid			nspOid;
-				ObjectAddress address;
 
 				address = get_object_address(stmt->objectType,
 											 stmt->object,