debian: Enable `Rules-Requires-Root: no`.

debian: Enable `Rules-Requires-Root: no`.

During a test rebuild for building packages with `Rules-Requires-Root:
no` as the default in `dpkg`, liblopsub failed to rebuild.

The problem is the rule of the `binary` target in `debian/rules` which
runs `install(1)` with -o root -g root to set the owner and group ID of
the files and directories being installed. With `Rules-Requires-Root:
no`, this fails due to insufficient permissions. This commit removes
the problematic options in favor of running `dh_fixperms(1)` just
before `dh_makeshlibs(1)`.

With these changes in place, the build no longer requires any form of
root during the `binary` target. Consequently, we may enable rootless
builds in `debian/control`.

Reported-by: Niels Thykier <niels@thykier.net>
Suggested-by: Niels Thykier <niels@thykier.net>
Reviewed--by: Niels Thykier <niels@thykier.net>