Remove unused Device Orientation code in Blink.

Remove old Device Orientation code because the new
implementation now lives in modules/device_orientation.
See crbug.com/261165 for a detailed migration process.

Chromium-side clean-up needs to land first:
https://codereview.chromium.org/25253003/

BUG=261165

Review URL: https://codereview.chromium.org/25295002

git-svn-id: svn://svn.chromium.org/blink/trunk@158874 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Move ContentType.cpp/.h to Source/platform/

BUG=297477

Review URL: https://codereview.chromium.org/25330002

git-svn-id: svn://svn.chromium.org/blink/trunk@158875 bbb929c8-8fbe-4397-9dbb-9b2b20218538