t5516 (fetch-push): drop implicit arguments from helper functions

Many of the tests in t5516 look like:

  mk_empty &&
  git push testrepo ... &&
  check_push_result $commit heads/master

It's reasonably easy to see what is being tested, with the
exception that "testrepo" is a magic global name (it is
implicitly used in the helpers, but we have to name it
explicitly when calling git directly). Let's make it
explicit when call the helpers, too. This is slightly more
typing, but makes the test snippets read more naturally.

It also makes it easy for future tests to use an alternate
or multiple repositories, without a proliferation of helper
functions.

[rr: fixed sloppy quoting]

Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Ramkumar Ramachandra <[email protected]>
Reviewed-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: peff