[analyzer] Clean up bug types in CallAndMessageChecker (#156073)
In CallAndMessageChecker the initialization of bug types was highly
obfuscated (even compared to other `mutable std::unique_ptr` hacks).
This commit cleans up this situation and removes a totally superfluous
hidded 'modeling' sub-checker that did not have any role apart from
obstructing the normal initialization of bug types.
(Note that if we need to reintroduce CallAndMessageModeling in the
future, we can do it cleanly within the CheckerFamily framework, so we
wouldn't need to re-obfuscate the bug type initialization.)
This change is mostly non-functional, the only visible change is the
removal of the hidden modeling checker.