Remove link to term that will later be defined in fetch

This commit can be reverted once whatwg/fetch#1540 lands

Author: jgraham

index.bs

@@ -4261,7 +4261,8 @@ To <dfn>get the base network event data</dfn> given |request| and |redirect coun
 
 1. Let |request data| be the result of [=get the request data=] with |request|.
 
-1. Let |navigation| be |request|'s [=request/navigation id=].
+<!-- TODO: update this to "[=request/navigation id=] once the fetch parts land-->
+1. Let |navigation| be |request|'s [=navigation id=].
 
 1. Let |context id| be null.