[eslint] no-useless-concat, no-useless-escape

.eslintrc.js

@@ -121,6 +121,8 @@ module.exports = {
         ],
         'no-unused-labels': 2,
         'no-useless-call': 2,
+        'no-useless-concat': 2,
+        'no-useless-escape': 2,
         'no-void': 2,
         'no-warning-comments': 0,
         'no-with': 2,

modules/xmpp/SDP.js

@@ -481,7 +481,7 @@ SDP.prototype.rtcpFbFromJingle = function(elem, payloadtype) { // XEP-0293
     let tmp = elem.find('>rtcp-fb-trr-int[xmlns="urn:xmpp:jingle:apps:rtp:rtcp-fb:0"]');
 
     if (tmp.length) {
-        media += 'a=rtcp-fb:' + '*' + ' ' + 'trr-int' + ' ';
+        media += 'a=rtcp-fb:* trr-int ';
         if (tmp.attr('value')) {
             media += tmp.attr('value');
         } else {

modules/xmpp/SDPUtil.js

@@ -8,6 +8,7 @@ const SDPUtil = {
     filter_special_chars(text) {
         // XXX Neither one of the falsy values (e.g. null, undefined, false,
         // "", etc.) "contain" special chars.
+        // eslint-disable-next-line no-useless-escape
         return text ? text.replace(/[\\\/\{,\}\+]/g, '') : text;
     },
     iceparams(mediadesc, sessiondesc) {