t5601: check ssh command only with protocol v0

t5601: check ssh command only with protocol v0

When running the SSH command as part of a fetch, Git will write "SendEnv
GIT_PROTOCOL" as an option if protocol v1 or v2 is used, but not v0.
Update all tests that check this to run Git with
GIT_TEST_PROTOCOL_VERSION=0.

I chose not to do a more thorough fix (for example, checking the value of
GIT_TEST_PROTOCOL_VERSION to see if the SendEnv check needs to be done)
because a set of patches [1] that unifies the handling of SSH options,
including writing "SendEnv GIT_PROTOCOL" regardless of protocol version,
is in progress. When that is done, this patch should be reverted, since
the functionality in here is no longer needed.

As of this patch, all tests pass if GIT_TEST_PROTOCOL_VERSION is set to
1.

[1] https://public-inbox.org/git/cover.1545342797.git.steadmon@google.com/

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>