package-source-builder: Drop the now-unused osc-setup

Since ci-package-builder!199


the CI pipeline is not using `osc-setup` anymore, so let's drop it.

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>

package-source-builder/overlay/usr/bin/osc-setup

-#!/bin/sh
-
-mkdir -p "$HOME"
-
-cat > ~/.oscrc <<EOF
-[general]
-apiurl = https://build.collabora.co.uk
-
-[https://build.collabora.co.uk]
-user = ${OSC_USERNAME}
-pass = ${OSC_PASSWORD}
-EOF