Remove deprecation warning from isConforming in default implementation

Summary

The default implementation of isConforming() redirected to the implementation class if it provides the method, otherwise return the static capability. This fallback implementation was deprecated to give the grid implementations a warning to provide their own implementation of isConforming(), but actually this fallback is the right form of implementing it and should not be marked as deprecated, it should not be removed in the future.

We now have two ways of asking for a grid property whether a gridview is conforming:

1. the static "always"-conforming property: Capability::is[Leaf|Level]WiseConforming
2. the dynamic (runtime) property gridView.isConforming() that might depend on other runtime flags in the grid.

If the grid is statically conforming, it is also dynamically conforming. If the static property is false, it could still be conforming but this can only be inspected at runtime.