This PR cleans up a plugin

- The plugin is not activated on doc-website, but it is usful and could be activated at some time.
- The patch makes it work
- It removes a redundant file

Website/plugins/link-error-test/config.raku

@@ -13,5 +13,5 @@
 	:run-tests,
 	:render,
 	:template-raku<let-templates.raku>,
-	:version<0.3.17>,
+	:version<0.3.18>,
 )

Website/plugins/link-error-test/let-callable.raku

@@ -20,6 +20,8 @@ sub ($pr, %processed, %options) {
     my %targets;
     #| possible filenames that map to a real html file
     my %aliases;
+    #| page names generated after LET plugin is called
+    my @structure-files;
 
     sub failed-targets($file, Str $target) {
         my $old = $target.trim;
@@ -90,8 +92,9 @@ sub ($pr, %processed, %options) {
         $resp
     }
     %aliases = %config<aliases>.kv.map({ '/' ~ $^a => '/' ~ $^b });
+    @structure-files = %config<structure-files>.map( '/' ~ * );
     #| SetHash of files in collection
-    my SetHash $files .= new( %aliases.keys );
+    my SetHash $files .= new( %aliases.keys.Slip, @structure-files.Slip );
     #| SetHash of files found missing
     my SetHash $missing .= new;
     my @remote-links;