DevTools: Get rid of frontend_modules.json

Instead, the compilation process will rely on module.json files that
all modules now have. Additionally, devtools.json lists all modules
that comprise the application.

R=pfeldman
BUG=391566

Review URL: https://codereview.chromium.org/573453004

git-svn-id: svn://svn.chromium.org/blink/trunk@182328 bbb929c8-8fbe-4397-9dbb-9b2b20218538