Fix rowversion code sample in 8.0 what's new docs

[roji]

Fixes #4725

[cremor]

This change doesn't actually improve any of my confusion described in issue #4725

Why do we need a HasConversion call? What does it do that isn't already done automatically when no HasConversion call is there at all?

[roji]

@ajcvickers can you take a quick look at all of this when you're back?

[ajcvickers]

@roji If the property is already a ulong, then specifying a conversion to ulong is pointless. If the conversion to byte[] is not now needed, that's great. I'm pretty sure last time I tested this, it was still needed in the fluent API.