Build: remove travis.yml and travis mentions from core (#4983)

We've migrated to GH actions on jQuery core and have already disabled travis builds for core.

Author: timmywil

.npmignore

@@ -4,7 +4,6 @@
 /.editorconfig
 /.gitattributes
 /.mailmap
-/.travis.yml
 
 /build
 /external

.travis.yml

@@ -22,7 +22,7 @@ module.exports = function( grunt ) {
 	var fs = require( "fs" ),
 		gzip = require( "gzip-js" ),
 		oldNode = /^v10\./.test( process.version ),
-		isCi = process.env.TRAVIS || process.env.GITHUB_ACTION,
+		isCi = process.env.GITHUB_ACTION,
 		ciBrowsers = process.env.BROWSERS && process.env.BROWSERS.split( "," );
 
 	if ( !grunt.option( "filename" ) ) {