fix(aio): remove links from sub-menu toggles (#21695)

Navigating to a document while trying to expand or collapse a sub-menu
is undesirable and confusing. All sub-menu toggles should have no other
effect than expanding/collapsing the corresponding sub-menu.

PR Close #21695

aio/content/navigation.json

@@ -74,7 +74,6 @@
     },
 
     {
-      "url": "tutorial",
       "title": "Tutorial",
       "tooltip": "The Tour of Heroes tutorial takes you through the steps of creating an Angular application in TypeScript.",
       "children": [
@@ -122,7 +121,6 @@
     },
 
     {
-      "url": "guide/architecture",
       "title": "Fundamentals",
       "tooltip": "The fundamentals of Angular",
       "children": [