Integrate meta-seconorth-distro/fngsystem-installation-overlays-fix

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Commit: seco-ne/yocto/layers/meta-seconorth-distro@ab2b6b4f

fngsystem-self-update: Handle left over 'overlays' text file from old installations

Prior versions of fngsystem used the overlays textfile, now we have an
overlays folder. This may disturb the copy overation so we delete it
in case it exists.