Revert "tty: add keypress event for backwards-compat"

In this case, backwards compatibility is not worth the API
inconsistency.  We can just document the change.

This reverts commit b521ff3b4f.

lib/tty.js

@@ -49,8 +49,6 @@ function ReadStream(fd) {
   this.readable = true;
   this.writable = false;
   this.isRaw = false;
-  // backwards-compat
-  require('readline').emitKeypressEvents(this);
 }
 inherits(ReadStream, net.Socket);