lib: remove dollar symbol for private function

Just remove '$' because this isn't a programming language like Python.

PR-URL: nodejs#25590
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

lib/events.js

@@ -93,14 +93,14 @@ EventEmitter.prototype.setMaxListeners = function setMaxListeners(n) {
   return this;
 };
 
-function $getMaxListeners(that) {
+function _getMaxListeners(that) {
   if (that._maxListeners === undefined)
     return EventEmitter.defaultMaxListeners;
   return that._maxListeners;
 }
 
 EventEmitter.prototype.getMaxListeners = function getMaxListeners() {
-  return $getMaxListeners(this);
+  return _getMaxListeners(this);
 };
 
 // Returns the length and line number of the first sequence of `a` that fully
@@ -247,7 +247,7 @@ function _addListener(target, type, listener, prepend) {
     }
 
     // Check for listener leak
-    m = $getMaxListeners(target);
+    m = _getMaxListeners(target);
     if (m > 0 && existing.length > m && !existing.warned) {
       existing.warned = true;
       // No error code for this since it is a Warning