bootctl,mute-console,pcrextend,pcrlock,repart: allow connections from self

bootctl,mute-console,pcrextend,pcrlock,repart: allow connections from self

With SD_VARLINK_SERVER_ROOT_ONLY, we refuse all unprivileged operations.
This is silly, the user can and should be able to do anything that doesn't
require privileges.

E.g.:

$ SYSTEMD_LOG_LEVEL=debug varlinkctl introspect /usr/lib/systemd/systemd-pcrextend
Forking off Varlink child process '/usr/lib/systemd/systemd-pcrextend'.
Successfully forked off '(sd-vlexec)' as PID 568993.
varlink: Setting state idle-client
json-stream: Sending message: {"method":"org.varlink.service.GetInterfaceDescription","parameters":{"interface":"io.systemd.PCRExtend"}}
Skipping PR_SET_MM, as we don't have privileges.
varlink: Changing state idle-client → calling
varlink: Unprivileged client attempted connection, refusing.
Failed to run Varlink event loop: Operation not permitted
json-stream: Got POLLHUP from socket.
varlink: Changing state calling → pending-disconnect
varlink: Connection was closed.
Failed to issue org.varlink.service.GetInterfaceDescription() varlink call: Connection reset by peer

This and similar commands now work, e.g.

$ SYSTEMD_LOG_LEVEL=debug varlinkctl call --more ./build/bootctl io.systemd.BootControl.ListBootEntries {}
...
Failed to open directory "/efi": No such file or directory
File system "/boot" is not a FAT EFI System Partition (ESP) file system.
...
Method call failed: Permission denied
{
	"origin" : "linux",
	"errno" : 13,
	"errnoName" : "EACCES"
}
Which is fine — we lack privileges to actually return a useful answer, but the
call itself should go through.

I didn't touch udevd, which refuses to run if it is not root, and does a lot of
privileged setup, so would refuse to start even if the check was removed.