Fix #10756 by removing some previously-obsoleted SignalR methods

[analogrelay]

Fixes #10756

In 3.0 we switched SignalR to use endpoint routing and obsoleted the old extension methods. This PR removes them.

[halter73]

+22 -403 👍

[analogrelay]

We don't have a provision for building the analyzer tests against older runtimes, though it might be feasible with TFM pivots. Doesn't feel super necessary though.

[ghost]

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[pranavkm]

Assert.Equal() Failure

↓ (pos 109)

Expected: ···erviceCollection.AddSignalR' inside the call to 'ConfigureSer···

Actual: ···erviceCollection.AddRouting' inside the call to 'ConfigureSer···

↑ (pos 109)


Stack trace
   at Microsoft.AspNetCore.SignalR.Tests.MapSignalRTests.<>c__DisplayClass1_0.<NotAddingSignalRServiceThrows>b__0(IApplicationBuilder app) in /_/src/SignalR/server/SignalR/test/MapSignalRTests.cs:line 49

[analogrelay]

@pranavkm dorp. I will do the needful ;).

[analogrelay]

I think this was because I incorrectly ported the NotAddingSignalRServiceThrows test to endpoint routing. Instead, I deleted it and renamed the old NotAddingSignalRServiceThrowsWhenUsingEndpointRouting test, since we don't need both anyway ;).

[ghost]

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