[clang] [libclang/python] Remove CompletionString.AvailabilityKindCompat (PR #210682)

[Vlad Serebrennikov via cfe-commits]

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@@ -58,6 +58,10 @@ latest release, please see the [Clang Web Site](https://clang.llvm.org) or the
 
 ### Clang Python Bindings Potentially Breaking Changes
 
+- `CompletionString.availability` now returns instances of `AvailabilityKind`.
+  As a result, the `__str__` representation of its return values changed.
+  It now follows the `CompletionChunkKind.VARIANT_NAME` scheme instead of `VariantName`, like other libclang enums. 
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Endilll wrote:

```suggestion
  Like other libclang enums, it now follows the `CompletionChunkKind.VARIANT_NAME` scheme instead of `VariantName`. 
```

https://github.com/llvm/llvm-project/pull/210682