Documents can specify their title via the `title` or `name` jsdoc tags.
This change adds that, if neither are provided, the first `<h1>` element
is removed from the `renderedContent` and used for the title.
If there is still no title then it is set to the empty string and a warning
is logged.
This reverts commit d0bc83ca27.
Protractor-based prerendering is flakey on Travis and takes several minutes to
complete, slowing down the build. Prerendering has a lower impact now that we
use a ServiceWorker. We will revisit in the future (probably using a
`PlatformServer`-based approach).
PR Close#15346