[css-navigation-1] Drop routemap integration for now, replacing it with an issue.

(This is part of importing the history from WICG/declarative-partial-updates.)

Author: dbaron

css-navigation-1/Overview.bs

@@ -82,9 +82,7 @@ with <<route-condition>> defined as:
 	<dfn><<route-in-parens>></dfn> = ( <<route-condition>> ) | ( <<route-test>> ) | <<general-enclosed>>
 	<dfn><<route-test>></dfn> = <<route-location>> | <<route-keyword>> : <<route-location>>
 	<dfn><<route-keyword>></dfn> = at | from | to
-	<dfn><<route-location>></dfn> = <<route-name>> | <<urlpattern()>>
-	<!-- TODO(dbaron): Should this be <<ident>> or <<custom-ident>> ? -->
-	<dfn><<route-name>></dfn> = <<custom-ident>>
+	<dfn><<route-location>></dfn> = <<urlpattern()>>
 </pre>
 
 The above grammar is purposely very loose for forwards-compatibility reasons,
@@ -97,11 +95,6 @@ is invalid.
 Style sheets <strong>must not</strong> use such a rule and
 processors <strong>must</strong> ignore such a rule (including all of its contents).
 
-A <<route-name>> is a reference to a route
-named in a <code highlight=html>&lt;script type=routemap></code>
-in the document.
-<span class="issue">This should be defined more formally once routemaps are.</span>
-
 Many of these grammar terms are associated with a boolean result,
 as follows:
 
@@ -203,18 +196,18 @@ as follows:
 The <dfn>route location URL pattern</dfn> of a <<route-location>>
 depends on the type of <<route-location>>:
 
-: <<route-name>>
-::	the URL pattern of a route named <<route-name>>
-	declared in a <code highlight=html>&lt;script type=routemap></code>.
-
-	ISSUE: Once routemaps are defined more formally,
-	this should be defined in terms of the routemap definition
-	instead of referring directly to URLPattern.
-
 : <<urlpattern()>>
 ::	The [=URL pattern=] represented by the function; see
 	[=create a URL pattern for urlpattern()=].
 
+ISSUE: There is currently only one type of <<route-location>>
+but we should consider adding another,
+which would be just a name that references
+a name defined in a routemap.
+See the
+<a href="https://github.com/WICG/declarative-partial-updates/blob/main/route-matching-explainer.md">route matching explainer</a>
+for details.
+
 A <dfn>document's navigation API</dfn> is
 the result of the following steps on <var>document</var>: