Refactor: controld: remove dead code

This is akin to already performed cleanups:

• fd89fcf9184b49fbd6193b2ee4710c6a8760b82b (cib/based)
• 6d0ffd3d85694719a0948e7353c75be69d9498bc (pengine/schedulerd)
• f0ff72901333a3e7e6e1531685bd347ea4861b4d + 5884db78080941cdc4e77499bc76677676729484 + eb7cce2a172a026336f4ba6c441dedce42f41092 [+ 19870cd6a62002864d380b54b416d9b9830b79ad + d9ab164e5b7867c15713b720e39152adcd8f2982] (pacemakerd)
• e94c02a567cf79318f3dc8da0317eac3ed39ecd0 (tengine, later merged with crmd/controld)

Note that the code appears to be a reuse of pre-existing heartbeat
sibling subproject, "application heatbeat ", see the freshly
resurrectected, git-converted original Mercurial repo:

https://gitlab.com/poki/archived-heartbeat/commit/a69bed5666374db138ea6f904842cbb80dbd0ceb
(Mercurial revision: 1708:7a672c022cbc)

and the realtime capabilities were in development in heartbeat since

https://gitlab.com/poki/archived-heartbeat/commit/68deb4b1406b23c2003ef80bc37d20d033369bb4
(Mercurial revision: 154:297f30ab2ecf)