qibuild.sh.install: remove dest when installing
qibuild.sh.install: remove dest when installing

This what `install` does, so it will let overwrite a read-only
file.
(`cp` won't do it, but we need to do it some time)

FIXME: maybe add a safe keyarg to install?

aldebaran/qibuild,dmerejkowsky/qibuild,dmerejkowsky/qibuild,dmerejkowsky/qibuild,dmerejkowsky/qibuild,aldebaran/qibuild,aldebaran/qibuild,aldebaran/qibuild,dmerejkowsky/qibuild