Chore: Revert "Add EnsureNoExportedKindName check"

[undef1nd]

Reverts this commit 0aae354

@sdboyer and I concluded that the check is too restrictive and does not add value, given that the Go compiler itself is enough to spot when the the CUE field name generates a Go type shadowing the package name.
Besides, both the generated types naming rule may change in the future.

[sdboyer]

thanks! it's a shame because this provided us a baseline for what i expect will be a validation pattern we'll want to follow in kindsys. But we'll get there :)