Remove CalleeParamsInfo

[jonmeow]

I'm seeing three issues with CalleeParamsInfo:

1. Although ResolveCalleeInCall had been extracted out and the EntityWithParamsBase could be used directly, that had not been cleaned up.
2. implicit_param_refs_id is unused; param_refs_id was only used by ResolveCalleeInCall. The factoring as a struct seems to be obscuring what's used and what isn't (creating unnecessary copies).
3. On Consolidate caller match in one function call #4446, CalleeParamsInfo seemed to be obfuscating what ConvertCallArgs actually worked with (a Function, not a generic entity).

I'm thinking that just removing CalleeParamsInfo is the best resolution here, it looks like it's tripping people up more than it's helping.

Note, I think Function used to be named Callable, which was where the "callable" name originally came from (I might be wrong about this). But "function" seems clearer about the type now.

[jonmeow]

Note, I was going back and forth about passing parameters individually versus just passing the Function as a whole, my leaning is towards the Function partly based on the way that'll resolve conflicts with #4446 (essentially, making return_slot_patterns_id part of the things implicitly passed)

[jonmeow]

This PR seems to have slipped through the cracks, maybe @geoffromer can review?