Remove screen-private-ppa test definition from contrib because it was added in base provider (Bugfix) (#2360)

Remove definition of screen-private-ppa from contrib pc-sanity because it was added in base provider and causes duplicate error (Bugfix)

Author: Artur-at-work

contrib/pc-sanity/units/pc-sanity/pc-sanity-screen-oem-gaps.pxu

@@ -16,16 +16,3 @@ _summary: check if pkgs are not supported by Canonical
 _description:
  This lists the packages which is not coming from main or restricted component.
 
-plugin: shell
-category_id: com.canonical.plainbox::miscellanea
-id: miscellanea/screen-private-ppa
-user: root
-command:
-  if grep -qrE 'private-ppa\.launchpad(|content)\.net' "/etc/apt/sources.list"* ; then
-      >&2 printf 'The following files have private PPA access:\n'
-      >&2 grep -lrE 'private-ppa\.launchpad(|content)\.net' "/etc/apt/sources.list"*
-      exit 1
-  fi
-_summary: check if any private ppas are added
-_description:
- This checks if any private ppas are added to the system, fails if any found.