refactor: remove the 'connecting' event

This event was added in 4195680

But it does not convey the information that the Socket is actually
sending a CONNECT packet to the server. It should maybe be moved to the
Socket#onopen() method, but let's remove it for now as it is not
documented anywhere.

lib/socket.ts

@@ -91,7 +91,6 @@ export class Socket extends Emitter {
     this.subEvents();
     if (!this.io.reconnecting) this.io.open(); // ensure open
     if ("open" === this.io.readyState) this.onopen();
-    super.emit("connecting");
     return this;
   }
 
@@ -101,7 +100,6 @@ export class Socket extends Emitter {
     this.subEvents();
     if (!this.io.reconnecting) this.io.open(); // ensure open
     if ("open" === this.io.readyState) this.onopen();
-    super.emit("connecting");
     return this;
   }