Delete empty non-ChromeOS log_private and diagnostics API implementations.

(Follows https://chromiumcodereview.appspot.com/26608002/)

Review URL: https://codereview.chromium.org/26628002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228122 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228122