Remove unused members from WebApplicationInfo.

Many of the members from WebApplicationInfo were in place to support
crx-less hosted apps. Since crx-less apps have been removed, we can
clean up references to them and repurpose convert_web_app.cc to be
solely for generating bookmark apps.

Review URL: https://codereview.chromium.org/142993002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247870 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247870