Fix generate_protocol_externs.py to stop appending "|undefined" suffices to array typedefs.

We used to have @typedef {!Array.<!type>|undefined} generated for many array typedefs.

R=apavlov

Review URL: https://codereview.chromium.org/111543004

git-svn-id: svn://svn.chromium.org/blink/trunk@163541 bbb929c8-8fbe-4397-9dbb-9b2b20218538