Aria-practices: Remove use of `rel` on `<ul>` and `<li>` elements in menubar/menubar-2/menubar-2.html

[nschonni]

This causes the validator to fail currently

"file:/Users/nschonni/Documents/github/aria-practices/examples/menubar/menubar-2/menubar-2.html":57.11-57.63: error: Attribute “rel” not allowed on element “ul” at this point.
"file:/Users/nschonni/Documents/github/aria-practices/examples/menubar/menubar-2/menubar-2.html":67.13-67.77: error: Attribute “rel” not allowed on element “li” at this point.
"file:/Users/nschonni/Documents/github/aria-practices/examples/menubar/menubar-2/menubar-2.html":68.13-68.79: error: Attribute “rel” not allowed on element “li” at this point.
"file:/Users/nschonni/Documents/github/aria-practices/examples/menubar/menubar-2/menubar-2.html":71.15-71.72: error: Attribute “rel” not allowed on element “ul” at this point.
"file:/Users/nschonni/Documents/github/aria-practices/examples/menubar/menubar-2/menubar-2.html":79.15-79.82: error: Attribute “rel” not allowed on element “ul” at this point.
"file:/Users/nschonni/Documents/github/aria-practices/examples/menubar/menubar-2/menubar-2.html":90.11-90.67: error: Attribute “rel” not allowed on element “ul” at this point.
"file:/Users/nschonni/Documents/github/aria-practices/examples/menubar/menubar-2/menubar-2.html":101.13-101.73: error: Attribute “rel” not allowed on element “li” at this point.
"file:/Users/nschonni/Documents/github/aria-practices/examples/menubar/menubar-2/menubar-2.html":102.13-102.73: error: Attribute “rel” not allowed on element “li” at this point.
"file:/Users/nschonni/Documents/github/aria-practices/examples/menubar/menubar-2/menubar-2.html":105.15-105.71: error: Attribute “rel” not allowed on element “ul” at this point.

Related to #779

To-do

• [ ] Land commit that removes rel attributes from ul/li elements
• [ ] Remove validator override for rel attribute on ul/li from .vnurc

[mcking65]

@jongund, What is the reason for using the rel attributes that are getting flagged by the validator? Could you change the implementation so they are not needed?

[carmacleod]

It looks like the rel attribute is just being used to store user metadata. It would be better to use a data- attribute. @jongund, I can take this if you like.