Revert the addition of libc6 to stage-packages for now. This will mak…

…e the snap unbuildable on bionic and beyond, but at least if it's built on xenial it will be working correctly on all other series. Hate classic confinement.

snapcraft.yaml

@@ -2,7 +2,7 @@ name: ubuntu-image
 summary: Create Ubuntu images
 description: |
   Use this tool to create Ubuntu images.
-version: 1.4+snap1
+version: 1.4+snap2
 grade: stable
 confinement: classic
 
@@ -31,7 +31,6 @@ parts:
       - dosfstools
       - e2fsprogs
       - fakeroot
-      - libc6
       - mtools
       - python3-debian
       - python3-git