rem: dev: remove CHECK_FOR_GLUE_IN_ANSWER

Macro CHECK_FOR_GLUE_IN_ANSWER is defined in `lib/dns/resolver.c` only,
documented nowhere and not exposed as build configuration. This is valid
at least for 9.21+, 9.20 and 9.18. Furthermore, it doesn't compile
anymore on 9.21+ with -DCHECK_FOR_GLUE_IN_ANSWER=1.

Considering it is very unlikely that anyone build named with this,
remove the code rather than fixing it.

Closes #5538

Merge branch '5538-remove-check-for-glue-in-answer' into 'main'

See merge request isc-projects/bind9!11029