Avoid creating unnecesary promises

by returning existing promises and by using _converse.api.sendIQ

src/converse-muc.js

@@ -471,13 +471,11 @@
                      *  A promise which resolves once the list has been
                      *  retrieved.
                      */
-                    return new Promise((resolve, reject) => {
                     affiliation = affiliation || 'member';
                     const iq = $iq({to: this.get('jid'), type: "get"})
                         .c("query", {xmlns: Strophe.NS.MUC_ADMIN})
                             .c("item", {'affiliation': affiliation});
-                        _converse.connection.sendIQ(iq, resolve, reject);
-                    });
+                    return _converse.api.sendIQ(iq);
                 },
 
                 setAffiliation (affiliation, members) {
@@ -678,16 +676,14 @@
                     if (_.isString(affiliations)) {
                         affiliations = [affiliations];
                     }
-                    return new Promise((resolve, reject) => {
                     const promises = _.map(
                         affiliations,
                         _.partial(this.requestMemberList.bind(this))
                     );
-                        Promise.all(promises).then(
-                            _.flow(u.marshallAffiliationIQs, resolve),
-                            _.flow(u.marshallAffiliationIQs, resolve)
+                    return Promise.all(promises).then(
+                        (iq) => u.marshallAffiliationIQs(iq),
+                        (iq) => u.marshallAffiliationIQs(iq)
                     );
-                    });
                 },
 
                 updateMemberLists (members, affiliations, deltaFunc) {