Add RUNTIME_CHECK() around result = dns_name_copy(..., NULL) calls

Add RUNTIME_CHECK() around result = dns_name_copy(..., NULL) calls

This second commit uses second semantic patch to replace the calls to
dns_name_copy() with NULL as third argument where the result was stored in a
isc_result_t variable.  As the dns_name_copy(..., NULL) cannot fail gracefully
when the third argument is NULL, it was just a bunch of dead code.

Couple of manual tweaks (removing dead labels and unused variables) were
manually applied on top of the semantic patch.

(cherry picked from commit 89b269b0d28e0acf4a1f92414b5df2e86e2a008e)