dns: rules files was not installed

Installed dns-events.rules files in rules directory with install-rules.
yaml: remove no more present files

emerging-virus.rules is not present anymore in ET ruleset downloaded
by 'make install-rules'. This patch removes it from the list to avoid
an error message.
erf-dag: fix typo in header guard

Spotted out by clang:
 source-erf-dag.h|25 col 9| warning: '__SOURCE_ERR_DAG_H__'
 is used as a header guard here, followed by #define of a different macro
 [-Wheader-guard]