This is a followup to 3794ce93be8216d8378df7b808ce7f53b1e05a53, which
broke command completion.
Reported by Oleg Pykhalov <go.wigust@gmail.com>.
* etc/completion/bash/guix (_guix_complete_command): Update to match
output of 'guix help' as introduced in
3794ce93be8216d8378df7b808ce7f53b1e05a53.