remote: usability: "diff" with no args makes nonsensical suggestion (--latest)

[edsantiago]

$ bin/podman-remote diff
Error: "podman-remote diff" requires a name, id, or the "--latest" flag

Solution: fix this to check for IsRemote()

podman/cmd/podman/diff/diff.go

Lines 75 to 77 in b8d95a5

	if len(args) == 0 && !given {
	return fmt.Errorf("%q requires a name, id, or the \"--latest\" flag", cmd.CommandPath())
	}