Use CSSJanus from upstream (v1.1.0)

Remove the local copy and include upstream instead.

Remove local unit tests as it's now a proper upstream lib that
is tested by uptream.

Release:

  https://github.com/cssjanus/php-cssjanus/releases/tag/v1.1.0

Changes:

  Features
  * Support "/*!" syntax for @noflip.
  * Flip border-style.

  Bug fixes
  * Improve flipping of background-position.
  * Restrict four_notation_quantity to margin, padding and border-width.
  * Flip two values in border-radius rule (in addition to four values).

Change-Id: Ieb6e179d6163f99a9c98fd99c2277d25135871fe