[LayoutReloaded] FloatingContext does not need a parent formatting context.

[LayoutReloaded] FloatingContext does not need a parent formatting context.
https://bugs.webkit.org/show_bug.cgi?id=184219

Reviewed by Antti Koivisto.

We don't need the formatting context in the FloatingContext now that margins are moved over to Display.Box.
This is in preparation for being able to create a FloatingContext for an inline formatting context,
when the inline context actually inherits the floating state from its formatting root.

* LayoutReloaded/FormattingContext/FloatingContext.js:
(FloatingContext):
(FloatingContext.prototype._availableSpace):
(FloatingContext.prototype._adjustedFloatingPosition):
(FloatingContext.prototype._addFloatingBox):
(FloatingContext.prototype._formattingContext): Deleted.
* LayoutReloaded/FormattingContext/FormattingContext.js:
(FormattingContext):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@230139 268f45cc-cd09-0410-ab3c-d52691b4dbfc