Following on from [1]:
- Since we're only ever calling _fully_qualified_name with module-level
functions, remove the ability to call it with a class (forcing such
usages to either use functions or modify this util).
- Consolidate a redundant invocation of _fully_qualified_name from
version_handler.
[1] Id8f96801116818dda6c68c301619aee185e8fbff
Change-Id: I205a7fd338a0db420b891341c3c40b10f3199fd3