Drop bin/tests/headerdep_test.sh.in, revise OPTIONS.md

bin/tests/headerdep_test.sh.in was apparently used to "Check the installed bind9 headers to make sure that no header depends on another header having been included first." It was created 20+ years ago, not really changed since, not plugged into configure.ac to generate the actual shell schript, and certainly not run in the CI.

This is a sample output:

 - <ns/xfrout.h>
In file included from test.c:1:
/tmp/bind9/include/ns/xfrout.h:29:14: error: unknown type name ‘ns_client_t’
   29 | ns_xfr_start(ns_client_t *client, dns_rdatatype_t xfrtype);
      |              ^~~~~~~~~~~
/tmp/bind9/include/ns/xfrout.h:29:35: error: unknown type name ‘dns_rdatatype_t’
   29 | ns_xfr_start(ns_client_t *client, dns_rdatatype_t xfrtype);
      |                                   ^~~~~~~~~~~~~~~

The 61a281b4 change is sparked by #1730 (closed).