bundle2: don't check for whether we can do stream clones
At the moment this isn't used and all stream clones use the legacy protocol.
In an upcoming diff, canperformstreamclone will print out a message if a stream
clone was requested but couldn't happen for some reason. Removing this call
ensures the message isn't printed twice.
#
# Avoid interference from actual test env:
unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL