Hide plumbing/transport commands from bash completion.

Hide plumbing/transport commands from bash completion.

Users generally are not going to need to invoke plumbing-level commands
from within one line shell commands.  If they are invoking these commands
then it is likely that they are glueing them together into a shell script
to perform an action, in which case bash completion for these commands is
of relatively little use.

Signed-off-by: Shawn O. Pearce <redacted>
Signed-off-by: Junio C Hamano <redacted>