Remove Travis config and badge (#2998)

Looks like our integration hasn't work for some time (since May or June 2021),
so these are no longer useful. We can replace this with GitHub actions in the
future, as other SDK teams have done.

Author: dagnir

.travis.yml

@@ -1,5 +1,5 @@
 # AWS SDK for Java 2.0
-[![Build Status](https://travis-ci.com/aws/aws-sdk-java-v2.svg?branch=master)](https://travis-ci.com/aws/aws-sdk-java-v2) ![Build Status](https://codebuild.us-west-2.amazonaws.com/badges?uuid=eyJlbmNyeXB0ZWREYXRhIjoiTFJSRXBBN1hkU1ZEQzZ4M1hoaWlFUExuNER3WjNpVllSQ09Qam1YdFlTSDNTd3RpZzNia3F0VkJRUTBwZlQwR1BEelpSV2dWVnp4YTBCOFZKRzRUR004PSIsIml2UGFyYW1ldGVyU3BlYyI6ImdHdEp1UHhKckpDRmhmQU4iLCJtYXRlcmlhbFNldFNlcmlhbCI6MX0%3D&branch=master)
+![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)