remove 'lxc config set <remote> password foo'

After talking with Serge this command is slightly non-sensical, and it confuses
other config options we'd like to have.

Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Merge pull request #54 from tych0/remove-set-remote

remove 'lxc config set <remote> password foo'