Hook module interface can be simplified after dropping support for statically linking named

The following discussion from !632 (closed) should be addressed:

• @michal started a discussion: (+5 comments)

  On Linux, if we enforced --with-libtool (which will soon be the case anyway due to Automake), the shared libraries loaded during named startup would be used for resolving symbols in modules loaded using dlopen() and thus the following would not be needed:

  • passing function pointers to query_done(), query_recurse(), log contexts, etc. through a struct ns_hookctx,
  • storing a function pointer to ns_hooktable_free() in struct dns_view,
  • the struct cfg_rep change from 822dc8be.

  We could even go a step further and drop the use of ${LIBS} for building modules.

  Are there platforms on which shared objects loaded using dlopen() are unable to look up symbols in other shared objects mapped into the same address space before them?