remove adhoc cache after adhoc-with-files cache has proven itself

[ThomasWaldmann]

master branch / betas:

"adhoc-with-files" is default since b9. "local" has been used before since ages (but with the known issues with chunks cache resyncing if multiple clients access the repo).

if there are no complaints about it, we can remove the adhoc implementation, which is basically the same (but much older, although likely nobody used it), but without the files cache (which makes it slow as it can't speedup unchanged files).