gcf2: wire up read-only daemons and rm -gcf2 script
It seems easiest to have a singleton Gcf2Client client object
per daemon worker for all inboxes to use. This reduces overall
FD usage from pipes.
The `public-inbox-gcf2' command + manpage are gone and a `$^X'
one-liner is used, instead. This saves inodes for internal
commands and hopefully makes it easier to avoid mismatched
PERL5LIB include paths (as noticed during development :x).
We'll also make the existing cat-file process management
infrastructure more resilient to BOFHs on process killing
sprees (or in case our libgit2-based code fails on us).
(Rare) PublicInbox::WWW PSGI users NOT using public-inbox-httpd
won't automatically benefit from this change, and extra
configuration will be required (to be documented later).