js: Convert people module to ES6.

frontend_tests/node_tests/composebox_typeahead.js

@@ -783,13 +783,12 @@ run_test("initialize", () => {
         assert.equal(appended_name, "Othello, the Moor of Venice");
 
         let appended_names = [];
-        people.get_by_user_id = function (user_id) {
+        people.__Rewire__("get_by_user_id", (user_id) => {
             const users = {100: hamlet, 104: lear};
             return users[user_id];
-        };
-        people.my_current_email = function () {
-            return "hamlet@zulip.com";
-        };
+        });
+
+        people.__Rewire__("my_current_email", () => "hamlet@zulip.com");
         compose_pm_pill.set_from_typeahead = function (item) {
             appended_names.push(item.full_name);
         };

frontend_tests/node_tests/people.js

@@ -737,20 +737,20 @@ run_test("extract_people_from_message", () => {
     assert(!people.is_known_user_id(maria.user_id));
 
     let reported;
-    people.report_late_add = function (user_id, email) {
+    people.__Rewire__("report_late_add", (user_id, email) => {
         assert.equal(user_id, maria.user_id);
         assert.equal(email, maria.email);
         reported = true;
-    };
+    });
 
     people.extract_people_from_message(message);
     assert(people.is_known_user_id(maria.user_id));
     assert(reported);
 
     // Get line coverage
-    people.report_late_add = function () {
+    people.__Rewire__("report_late_add", () => {
         throw Error("unexpected late add");
-    };
+    });
 
     message = {
         type: "private",

frontend_tests/node_tests/people_errors.js

@@ -104,12 +104,8 @@ run_test("blueslip", () => {
     const reply_to = people.pm_reply_to(message);
     assert(reply_to.includes("?"));
 
-    people.pm_with_user_ids = function () {
-        return [42];
-    };
-    people.get_by_user_id = function () {
-        return;
-    };
+    people.__Rewire__("pm_with_user_ids", () => [42]);
+    people.__Rewire__("get_by_user_id", () => {});
     blueslip.expect("error", "Unknown people in message");
     const uri = people.pm_with_url({});
     assert.equal(uri.indexOf("unk"), uri.length - 3);