Remove shadow layer (more dead code).

This looked suspiciously like it was drawing the shadow for the linen
background, but it turned out to be doing nothing.

BUG=133097

Review URL: https://chromiumcodereview.appspot.com/22312003

git-svn-id: svn://svn.chromium.org/blink/trunk@155651 bbb929c8-8fbe-4397-9dbb-9b2b20218538