contrib: drop blameview/ directory

Blameview was a quick-and-dirty demonstration of how blame's
incremental output could be used in an interface. These days
one can find much better (and less ugly!) demonstrations in
"git gui blame" and "tig blame".

The only advantage blameview has is that its code is perhaps
simpler to read. However, that is balanced by the fact that
it probably has bugs, as nobody uses it nor has touched the
code in 6 years. An implementor is probably better off just
reading the "incremental output" section of "man git-blame".

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>