contrib: git-remote-{bzr,hg} placeholders don't need Python

contrib: git-remote-{bzr,hg} placeholders don't need Python

It does not make sense for these placeholder scripts to depend on Python
just because the real scripts do. At the example of Git for Windows, we
would not even be able to see those warnings as it does not ship with
Python. So just use plain shell scripts instead.

Signed-off-by: Sebastian Schuberth <redacted>
Reviewed-by: Jeff King <redacted>
Signed-off-by: Junio C Hamano <redacted>