setup: stop using `the_repository` in `check_repository_format()`

setup: stop using `the_repository` in `check_repository_format()`

Stop using `the_repository` in `check_repository_format()` and instead
accept the repository as a parameter. The injection of `the_repository`
is thus bumped one level higher, where callers now pass it in
explicitly.

Furthermore, the function is never used outside "setup.c". Drop its
declaration in "setup.h" and make it static. Note that this requires us
to reorder the function.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>