t: use test_seq -f and pipes in a few more places

t: use test_seq -f and pipes in a few more places

Several tests use a pattern that writes to a temporary file like this:

  printf "do something with %d\n" $(test_seq <count>) >tmpfile &&
  git do-something --stdin <tmpfile

Other tests use test_seq's -f parameter, but still write to a temporary file:

  test_seq -f "do something with %d" <count> >input &&
  git do-something --stdin <input

Simplify both of these patterns to

  test_seq -f "do something with %d" <count> |
  git do-something --stdin

Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>