[web-animations-2] Define a title as in other specs

[lahmatiy]

That's a single spec that define a title via <h1>. Now it defined as in any other spec

[lahmatiy]

Marked as non substantive for IPR from ash-nazg.

[tabatkins]

(Note that the old form is perfectly okay per Bikeshed; it looks for the first h1 and takes it as the title of the spec if no Title metadata is present. It's also required if you want to put markup in your title. But I do prefer keeping things similar in structure when possible.)