desktop-shell: Delete Exposay

Exposay was done as a showcase for what we could do with Weston and an efficient compositing pipeline. This was mostly with the old vendor-specific Raspberry Pi backend which could actually process that many surfaces bypassing the GPU.

Given enough bitrot, Exposay is now pretty exemplary as what not to do in a Weston shell - particularly the way it manipulates existing weston_views rather than create its own non-destructive stack.

As it's annoying technical debt, a terrible example to others, and not a very compelling showcase in 2022, just delete it.

Signed-off-by: Daniel Stone daniels@collabora.com