Remove #[abi = "foo"] attributes from codebase.

[luqmana]

They no longer play any role in determining abi choice and just end up confusing people. If necessary they should just be replaced with the (relatively) new syntax: extern "foo" { ... }.

[wakandan]

I found quite a number of places where this bit happens. What tests should I run to make sure what I changed is working?

[wakandan]

above is the new commit I made