Remove erroneous SCRIPT elements in LayoutTests/editing/{spelling,text-iterator}

This patch removes script elements which refer non-existing-file, "resources/js-test-selection-shared.js" in LayoutTest/editing/{spelling,text-iterator}. Failure of loading script file isn't in TestRunner output and doesn't cause test failure. Although, is is confusing to test maintainer.

BUG=n/a
TEST=n/a; no behavior changes

Review URL: https://codereview.chromium.org/90353004

git-svn-id: svn://svn.chromium.org/blink/trunk@162749 bbb929c8-8fbe-4397-9dbb-9b2b20218538