Simplify the Incognito NTP.

Reduce the amount of text.

BUG=70664
TEST=none
R=somast@google.com

Review URL: https://codereview.chromium.org/101533003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239282 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239282