util: move custom inspection function to EOL

Move the use of custom inspection function to End-of-Life.

Ref: nodejs#15549

Author: Trott

doc/api/deprecations.md

@@ -718,7 +718,7 @@ Type: Runtime
 <a id="DEP0079"></a>
 ### DEP0079: Custom inspection function on Objects via .inspect()
 
-Type: Runtime
+Type: End-of-Life
 
 Using a property named `inspect` on an object to specify a custom inspection
 function for [`util.inspect()`][] is deprecated. Use [`util.inspect.custom`][]