Ratify the extended-monitor specification. (#508)

Author: sadiepowell

extensions/extended-monitor.md

@@ -1,7 +1,6 @@
 ---
 title: "`extended-monitor` Extension"
 layout: spec
-work-in-progress: true
 extends:
   - monitor
   - away-notify
@@ -15,19 +14,6 @@ copyrights:
     period: "2021"
 ---
 
-
-## Notes for implementing work-in-progress version
-
-This is a work-in-progress specification.
-
-Software implementing this work-in-progress specification MUST NOT use the
-unprefixed `extended-monitor` capability name. Instead, implementations SHOULD
-use the `draft/extended-monitor` capability name to be interoperable with other
-software implementing a compatible work-in-progress version.
-
-The final version of the specification will use an unprefixed capability name.
-
-
 ## Description
 
 With the help of extensions such as [`away-notify`](away-notify.html),