environment: stop using `the_repository` in `is_bare_repository()`

environment: stop using `the_repository` in `is_bare_repository()`

Refactor `is_bare_repository()` to take in a repository parameter so
that we no longer depend on `the_repository`. Adjust callers
accordingly.

Furthermore, move the function outside of the declarations that are only
available when `USE_THE_REPOSITORY_VARIABLE` is set, as it no longer
depends on that variable.

Signed-off-by: Patrick Steinhardt <redacted>
Signed-off-by: Junio C Hamano <redacted>