Remove dead code in Forms area.

This CL removes the followings:
HTMLFieldSetElement::length
HTMLFormElement::formWouldHaveSecureSubmission
HTMLFormElement::setAction
HTMLInputElement::isColorControl declaration
HTMLInputElement::isSubmitButton declaration
HTMLSelectElement::deselectItems
PopupMenuClient::createScrollbar
PopupMenuClient::fontSelector
PopupMenuClient::hostWindow
PopupMenuClient::valueShouldChangeOnHotTrack
PopupMenuStyle::textIndent
RenderMenuList::createScrollbar
RenderMenuList::fontSelector
RenderMenuList::hostWindow
RenderMenuList::valueShouldChangeOnHotTrack

BUG=none
TEST=none; no behavior changes.

Review URL: https://codereview.chromium.org/136473009

git-svn-id: svn://svn.chromium.org/blink/trunk@165308 bbb929c8-8fbe-4397-9dbb-9b2b20218538