Clean up chardev sockets on QEMU shutdown

https://bugzilla.redhat.com/show_bug.cgi?id=1088787

Clean up unix socket files for chardevs using mode='bind',
like we clean up the monitor socket.
They are created by QEMU on startup and not really useful
after shutting it down.
Fix an extra ' in a translated string

Raised by ukrainian translator Yuri Chornoivan
https://fedora.transifex.com/projects/p/libvirt/translate/#uk/strings/25483059