Merge grub-pc-removal-cherrypick-focal into focal [a=patviafore] [r=codyshepherd,philroche]

Cherry-pick grub-pc removal.

Azure wants the grub-pc change by the end of the month, and the SRU
process will not be finished by then. Cherry-picking the change to our
team fork while waiting for the actual change to land.

MP: https://code.launchpad.net/~patviafore/livecd-rootfs/+git/livecd-rootfs/+merge/394431

debian/changelog

@@ -1,3 +1,11 @@
+livecd-rootfs (2.664.8.1) focal; urgency=medium
+
+   [ Dimitri John Ledkov & Joshua Powers ]
+   * amd64: always install grub-pc with shim-signed (LP: #1901906), and
+     ensure to autoremove packages
+
+ -- Robert C Jennings <robert.jennings@canonical.com>  Fri, 20 Nov 2020 15:08:54 -0600
+
 livecd-rootfs (2.664.8) focal; urgency=medium
 
   Backport snap-preseed work from groovy to focal LP: #1896755