Inconsistent naming recommendation for XRD kind

[eric-carlsson]

URL

https://docs.crossplane.io/latest/composition/composite-resource-definitions/#xrd-names

What's Wrong?

In Crossplane v2 there are no more claims, so there's no longer a need to add an "X" prefix to differentiate claims from XRs. The v2 docs were updated to reflect this in 66ca410 etc., but the XRD page still documents the old naming recommendation, and also does so in an inconsistent manner.

Specifically, this needs to be updated:

docs/content/v2.1/composition/composite-resource-definitions.md

Lines 120 to 123 in 15fb38a

	* `kind` - the `kind` value to use when calling this API. The kind is
	[UpperCamelCased](https://kubernetes.io/docs/contribute/style/style-guide/#use-upper-camel-case-for-api-objects).
	Crossplane recommends starting XRD `kinds` with an `X` to show
	it's a custom Crossplane API definition.

As well as examples throughout the page.