Remove Gitter badge/link (#5591)

Gitter is no longer actively monitored; GitHub Discussion is preferred.

CONTRIBUTING.md

@@ -99,10 +99,9 @@ Please keep the following in mind when considering a code contribution:
   be assigned to it.
 
   If you are thinking about adding entirely new functionality, open a [Feature
-  Request](#feature-requests) or [ping][gitter] the maintainers to ask for
-  feedback first before beginning work; again this is to make sure that no one
-  else is already working on it, and also that it makes sense to be included in
-  the SDK.
+  Request](#feature-requests) to ask for feedback first before beginning work;
+  again this is to make sure that no one else is already working on it, and
+  also that it makes sense to be included in the SDK.
 * All code contributions must be accompanied with new or modified tests that
   verify that the code works as expected; i.e. that the issue has been fixed or
   that the functionality works as intended.
@@ -162,6 +161,5 @@ when contributing to the SDK.
 [label-doc-issue]: https://github.com/aws/aws-sdk-java-v2/labels/documentation
 [label-feature-request]: https://github.com/aws/aws-sdk-java-v2/labels/feature-request
 [git-rewriting-history]: https://git-scm.com/book/en/v2/Git-Tools-Rewriting-History
-[gitter]: https://gitter.im/aws/aws-sdk-java-v2
 [bug-report]: https://github.com/aws/aws-sdk-java-v2/issues/new?assignees=&labels=bug%2Cneeds-triage&template=bug-report.yml&title=%28short+issue+description%29
 [feature-request]: https://github.com/aws/aws-sdk-java-v2/issues/new?assignees=&labels=feature-request%2Cneeds-triage&template=feature-request.yml&title=%28short+issue+description%29

README.md

@@ -1,7 +1,6 @@
 # AWS SDK for Java 2.0
 ![Build Status](https://codebuild.us-west-2.amazonaws.com/badges?uuid=eyJlbmNyeXB0ZWREYXRhIjoiTFJSRXBBN1hkU1ZEQzZ4M1hoaWlFUExuNER3WjNpVllSQ09Qam1YdFlTSDNTd3RpZzNia3F0VkJRUTBwZlQwR1BEelpSV2dWVnp4YTBCOFZKRzRUR004PSIsIml2UGFyYW1ldGVyU3BlYyI6ImdHdEp1UHhKckpDRmhmQU4iLCJtYXRlcmlhbFNldFNlcmlhbCI6MX0%3D&branch=master)
 [![Maven](https://img.shields.io/maven-central/v/software.amazon.awssdk/s3.svg?label=Maven)](https://search.maven.org/search?q=g:%22software.amazon.awssdk%22%20AND%20a:%22s3%22)
-[![Gitter](https://badges.gitter.im/aws/aws-sdk-java-v2.svg)](https://gitter.im/aws/aws-sdk-java-v2?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge) 
 [![codecov](https://codecov.io/gh/aws/aws-sdk-java-v2/branch/master/graph/badge.svg)](https://codecov.io/gh/aws/aws-sdk-java-v2)
 <!-- ALL-CONTRIBUTORS-BADGE:START - Do not remove or modify this section -->
 [![All Contributors](https://img.shields.io/badge/all_contributors-111-orange.svg?style=flat-square)](#contributors-)
@@ -173,7 +172,6 @@ We need your help in making this SDK great. Please participate in the community
 [sdk-website]: http://aws.amazon.com/sdkforjava
 [aws-java-sdk-bom]: https://github.com/aws/aws-sdk-java-v2/tree/master/bom
 [stack-overflow]: http://stackoverflow.com/questions/tagged/aws-java-sdk
-[gitter]: https://gitter.im/aws/aws-sdk-java-v2
 [features]: https://github.com/aws/aws-sdk-java-v2/issues?q=is%3Aopen+is%3Aissue+label%3A%22feature-request%22
 [support-center]: https://console.aws.amazon.com/support/
 [console]: https://console.aws.amazon.com