Revert "Merge pull request #12208 from mjhoy/patch-1"

This reverts commit ab5cd54b7e, reversing
changes made to cdc10c898d.

Reason: This way of defining root path is still supported. See
d262773ab7/actionpack/test/controller/routing_test.rb (L450-457)

actionpack/lib/action_dispatch/routing/mapper.rb

@@ -319,6 +319,10 @@ module ActionDispatch
         #
         # For options, see +match+, as +root+ uses it internally.
         #
+        # You can also pass a string which will expand
+        #
+        #   root 'pages#main'
+        #
         # You should put the root route at the top of <tt>config/routes.rb</tt>,
         # because this means it will be matched first. As this is the most popular route
         # of most Rails applications, this is beneficial.