Remove obsolete test cases

With the move away from a patched WebKit2GTK+ to an upstream version,
some features have been lost and there is no need (or way) to test them
anymore.

actor-tiles: no longer uses Clutter, the backing store does not use
Clutter actors anymore, that was a custom change

aligned-scroll: heuristic alignment lock of panning was a custom feature
which is not present upstream; upstream only supports setting the
direction lock before the pan starts

contextual-zoom: contextual zoom was a custom feature not available
upstream; it is not as important currently, though, since most pages are
now designed to be touchscreen friendly

lazy-click: also known as touch adjustment, it was also a custom feature
not available upstream; like contextual-zoom, it is not as relevant
nowadays, as sites are designed to be touch-friendly