fix: do not reset the ping timer after upgrade

There was two issues with this behavior:

- v3 clients (with allowEIO3: true) were also receiving a "ping" after
a successful upgrade, which is incorrect (in v3, it's the client that
sends the "ping", and the server answers with a "pong")

- the ping timer is not reset after upgrade on the client-side, so an
upgrade which took longer than the `pingTimeout` duration could lead to
a "ping timeout" error on the client-side

I think the latter issue is present since the initial implementation.

Related: socketio/socket.io-client-swift#1309 (comment)

lib/socket.js

@@ -237,7 +237,6 @@ class Socket extends EventEmitter {
         self.clearTransport();
         self.setTransport(transport);
         self.emit("upgrade", transport);
-        self.schedulePing();
         self.flush();
         if (self.readyState === "closing") {
           transport.close(function() {

test/server.js

@@ -1282,6 +1282,24 @@ describe("server", () => {
       });
     });
 
+    it("should not timeout after an upgrade", done => {
+      const opts = { pingInterval: 200, pingTimeout: 20 };
+      const engine = listen(opts, port => {
+        const socket = new eioc.Socket("ws://localhost:%d".s(port));
+        socket.on("open", () => {
+          setTimeout(() => {
+            socket.removeListener("close");
+            engine.close();
+            socket.close();
+            done();
+          }, 500);
+        });
+        socket.on("close", () => {
+          done(new Error("should not happen"));
+        });
+      });
+    });
+
     it("should not crash when messing with Object prototype", done => {
       Object.prototype.foo = "bar"; // eslint-disable-line no-extend-native
       const engine = listen({ allowUpgrades: true }, port => {