kamailio-5.x: add new modules + cleanup

kamailio-5.x: add new modules + cleanup

From upstream release notes:

Six new modules:

 - app_lua_sr – old Lua API before introduction of KEMI
 - lost – HELD (RFC6155) and LOST (RFC5222) location-based routing
 - kemix – KEMI specific extensions
 - rtp_media_server – embedded RTP and media processing
   functionalities for Kamailio (like playing media or bridging in a
   B2BUA manner, includes support for different codecs, including Opus)
 - secfilter – filters to allow/block using whitelists/blacklist based
   on user agents, IP addresses, countries, domains and users
 - xhttp_prom – generates suitable metrics for a Prometheus monitoring
   platform, answering to Prometheus pull requests

Additionally this removes libxml2 dependency from modules, because base
kamailio package already depends on it.

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>