Remove ENABLE_NEW_GAMEPAD_API #ifdefs

Remove ENABLE_NEW_GAMEPAD_API #ifdefs now that the chromium side has been
updated and now that the flag is turned on by default.

R=eseidel@chromium.org
BUG=344556

Review URL: https://codereview.chromium.org/302563003

git-svn-id: svn://svn.chromium.org/blink/trunk@174781 bbb929c8-8fbe-4397-9dbb-9b2b20218538