timers: reposition getTimers definition internally

Just cleanup so the file makes more future sense.

PR-URL: #18065
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>

lib/internal/timers.js

@@ -29,6 +29,14 @@ module.exports = {
   validateTimerDuration
 };
 
+var timers;
+function getTimers() {
+  if (timers === undefined) {
+    timers = require('timers');
+  }
+  return timers;
+}
+
 // Timer constructor function.
 // The entire prototype is defined in lib/timers.js
 function Timeout(callback, after, args, isRepeat) {
@@ -66,13 +74,6 @@ function Timeout(callback, after, args, isRepeat) {
   }
 }
 
-var timers;
-function getTimers() {
-  if (timers === undefined) {
-    timers = require('timers');
-  }
-  return timers;
-}
 
 function setUnrefTimeout(callback, after, arg1, arg2, arg3) {
   // Type checking identical to setTimeout()