MEDIUM: cli/show-fd: no longer accept filtering for dispatch mode

MEDIUM: cli/show-fd: no longer accept filtering for dispatch mode

"show fd" supports various flags, one of which is 'd' for "dispatch",
which also catches "transparent", in fact, connections whose target is
a proxy. Since these can no longer happen, let's remove that. The 'b'
and 's' flags are now aliases of each other for simplicity.