Remove obsoleted XmlPoke Aliases

[devlead]

As discussed in #974 it's now time to remove the obsoleted XmlPoke aliases.

[gep13]

@devlead If you want the Breaking Change label to appear in the release notes, which i think is a good idea, we will need to add the label to the GitReleaseManager.yaml file, so that it picks it up.

[devlead]

@gep13 agree, should I send a separate pr/issue there?

[gep13]

@devlead yes, I think that would be justified, yes.

[devlead]

@gep13 cool, I'll fix that shortly.

[devlead]

@gep13 #979 should be ready for review as is then.

[gep13]

@devlead I think it was mentioned elsewhere as well, but just to recap... I think we need a new page on the website that lists when Aliases were obsoleted, i.e. in what version of Cake. And we can keep a track of things there, so that we can point people to.

i.e. when method was added, when it was obsoleted, and when it was removed.

Thoughts?

[patriksvensson]

@gep13 @devlead Yes, I think this is a good idea. Actually, we could create our own ObsoleteAttribute as well with this information and generate it from the NuGet package.

[devlead]

We could use something like Particular Software API comparer to diff public APIs between versions.