Docserver: Strip extension from template filenames on presubmit

Because the docserver now redirects foo.html to foo, presubmit tests
have been changed to query extensionless URLs for corresponding template
files.

BUG=343614
R=kalman@chromium.org

Review URL: https://codereview.chromium.org/164493004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251158 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251158