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
Gaining access to another PR's JWT, would allow faking that PR's author wrt to
GitHub team membership verification for as long as the JWT is valid (currently
90 mins).