Revert home/tabzilla MWC promos. Bug 984598.

- Tabzilla promo was reverted in previous commit. This
  commit removes the no longer used tabzilla MWC image
  and tabzilla MWC CSS.
Merge pull request #1790 from jpetto/bug-984598-revert-home-tabzilla-promos

Revert home/tabzilla MWC promos. Bug 984598.