Remove gitter from readme (#114841)

* Remove gitter from readme

Last activity there was years ago, the community is on discord.

* Update docs/workflow/ci/failure-analysis.md

Co-authored-by: Jan Kotas <[email protected]>

---------

Co-authored-by: Jan Kotas <[email protected]>

Author: akoeplinger

README.md

@@ -3,7 +3,6 @@
 [![Build Status](https://dev.azure.com/dnceng-public/public/_apis/build/status/dotnet/runtime/runtime?branchName=main)](https://dev.azure.com/dnceng-public/public/_build/latest?definitionId=129&branchName=main)
 [![Help Wanted](https://img.shields.io/github/issues/dotnet/runtime/help%20wanted?style=flat-square&color=%232EA043&label=help%20wanted)](https://github.com/dotnet/runtime/labels/help%20wanted)
 [![Good First Issue](https://img.shields.io/github/issues/dotnet/runtime/good%20first%20issue?style=flat-square&color=%232EA043&label=good%20first%20issue)](https://github.com/dotnet/runtime/labels/good%20first%20issue)
-[![Gitter](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/dotnet/runtime)
 [![Discord](https://img.shields.io/discord/732297728826277939?style=flat-square&label=Discord&logo=discord&logoColor=white&color=7289DA)](https://aka.ms/dotnet-discord)
 
 * [What is .NET?](#what-is-net)

docs/workflow/ci/failure-analysis.md

@@ -57,7 +57,7 @@ Validation may fail for several reasons, and for each one we have a different re
 
 ### Additional information:
   * If the license/cla check fails to register a response, the check can be rerun by submitting a `@dotnet-policy-service rerun` comment to the PR.
-  * Reach out to the infrastructure team for assistance on [Teams channel](https://teams.microsoft.com/l/channel/19%3ab27b36ecd10a46398da76b02f0411de7%40thread.skype/Infrastructure?groupId=014ca51d-be57-47fa-9628-a15efcc3c376&tenantId=72f988bf-86f1-41af-91ab-2d7cd011db47) (for corpnet users) or on [Gitter](https://gitter.im/dotnet/community) in other cases.
+  * Reach out to the infrastructure team for assistance on [Teams channel](https://teams.microsoft.com/l/channel/19%3ab27b36ecd10a46398da76b02f0411de7%40thread.skype/Infrastructure?groupId=014ca51d-be57-47fa-9628-a15efcc3c376&tenantId=72f988bf-86f1-41af-91ab-2d7cd011db47) (for corpnet users) or on [Discord](https://aka.ms/dotnet-discord) #runtime channel in other cases.
 
 ## What to do if you determine the failure is unrelated