[SignalR] Remove obsolete APIs

[BrennanConroy]

Part of #27529

Both APIs already throw when used. The ParseResponse method was obsoleted in 3.1, HubInvocationContext.ctor was obsoleted in 5.0.

I have seen no evidence of anyone using HubInvocationContext.ctor and there wasn't a good reason to use it before 5.0 (Hub filters).

I have seen one place using ParseResponse, but the newest version of the package uses the non-obsolete method.

[davidfowl]

Beautiful

[halter73]

Normally, I would say why break it? But since this basically just changes a NotSupportedException to a MethodMissingException for libraries, and it makes what could be an annoying runtime error into a compile-time error for projects that are rebuilding anyway, this makes a lot of sense.

[ghost]

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