Ditch DictImp GetEnumerator<T> code that was needed because of a runtime bug

[T-Gro]

This bug has been fixed in the meantime.
Original issue:
F#: #5910
Runtime: dotnet/runtime#11488

Resolution in runtime repo:
dotnet/coreclr#21368

Tests:

[vzarytovskii]

So, what happens if FSharp.Core with this change is loaded into runtime with bug present? Or was the fix backported to all branches?

[T-Gro]

So, what happens if FSharp.Core with this change is loaded into runtime with bug present? Or was the fix backported to all branches?

The worst case is that repeated access to .Current after enumeration has finished (MoveNext() returned false) will not throw.

I tried searching trough the runtime repo, but I do not see links which would tell me which versions this went into.
I can only see it is a little over 4 years ago since it was merged to main.
dotnet/coreclr#21368

[T-Gro]

But since it was 4 years ago, it means that versions 6 and 7 have it (the only supported versions as of now?).