ash: Remove some dead code.

ShelfLayoutManager::GetInsetsForAlignment() is no longer used.

BUG=318879
R=skuhne@chromium.org

Review URL: https://codereview.chromium.org/167373006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253050 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253050