Remove 0.62 lookup compatibility code from classes

[freider]

Removing some of the more obvious 0.62 compatibility layers from the Cls/Obj code, now that 0.62 is EOL

I think there are more opportunities for refactoring/simplification of the class code that requires some more careful consideration, and once 0.67 is the minimum version we can probably remove a whole lot more (we wouldn't even need backend "class" objects at that point.)

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Check these boxes or delete any item (or this section) if not relevant for this PR.

• Client+Server: this change is compatible with old servers
• Client forward compatibility: this change ensures client can accept data intended for later versions of itself

Note on protobuf: protobuf message changes in one place may have impact to
multiple entities (client, server, worker, database). See points above.

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Changelog

[freider]

@prbot approve

[modal-pr-review-automation]

Approved 👍. @devennavani will follow-up review this.

[erikbern]

could maybe just rename it _function.py now. I think we called it functions.py because the name clashed with something

[freider]

could maybe just rename it _function.py now. I think we called it functions.py because the name clashed with something

Yeah the internal one can easily be renamed. The "public" functions.py need some deprecation first since we use modal.functions.FunctionCall references not going via the top level modal package sometimes in our examples :(