c/cruft: Stop relying on file(1) on (partial) text files

While there is nothing wrong with relying on file(1), the "ascii" test
in file(1) is fairly expensive.

Signed-off-by: Niels Thykier <niels@thykier.net>
coll/file-info: Pass "-e ascii" to file(1)

Disable the file "ascii" test.  A quick test suggests that -e ascii
reduces the runtime of file-info on source:linux by about 100s
(117s -> 20s).  Since nothing in Lintian currently relies on this
file(1) test, disabling it is simply a "free optimization".

Signed-off-by: Niels Thykier <niels@thykier.net>