receive.fsck.<msg-id> tests: remove dead code

receive.fsck.<msg-id> tests: remove dead code

Remove the setting of a receive.fsck.badDate config variable to
"ignore". This was added in efaba7cc77 ("fsck: optionally ignore
specific fsck issues completely", 2015-06-22) but never did anything,
presumably it was part of some work-in-progress code that never made
it into git.git.

None of these tests will emit the "invalid author/committer line - bad
date" warning. The dates on the commit objects we're setting up are
not invalid.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>