Fix file comment for test_rls_hooks.c

The file-level comment wasn't updated when it was copied from the shared
memory queue test module.  Fixed.

Noted by Dean Rasheed.

src/test/modules/test_rls_hooks/test_rls_hooks.c

 /*--------------------------------------------------------------------------
  *
- * test.c
- *		Test harness code for shared memory message queues.
+ * test_rls_hooks.c
+ *		Code for testing RLS hooks.
  *
  * Copyright (C) 2015, PostgreSQL Global Development Group
  *