Delete old omnibox border assets.

Delete the omnibox_border, omnibox_popup_border, and touch
omnibox_filling images. New omnibox_border_and_shadow /
omnibox_popup_border_and_shadow images are used instead now.

BUG=233364
TBR=oshima@chromium.org

Review URL: https://codereview.chromium.org/116193004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242630 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242630