doc: remove os.uptime() Windows note

The libuv 1.20.2 update in Node 10 aligned the Windows behavior
of os.uptime() with that of other operating systems. The return
value no longer contains a fraction component.

Refs: nodejs#20129

doc/api/os.md

@@ -381,15 +381,17 @@ systems.
 ## os.uptime()
 <!-- YAML
 added: v0.3.3
+changes:
+  - version: v10.0.0
+    pr-url: https://github.com/nodejs/node/pull/20129
+    description: The result of this function no longer contains a fraction
+                 component on Windows.
 -->
 
 * Returns: {integer}
 
 The `os.uptime()` method returns the system uptime in number of seconds.
 
-On Windows the returned value includes fractions of a second. Use `Math.floor()`
-to get whole seconds.
-
 ## os.userInfo([options])
 <!-- YAML
 added: v6.0.0