Grub: Purge grub-pc before installing grub-efi-amd64

Purging grub-pc removes /etc/default/grub
Installing grub-efi-amd64 recreates it..

if we purge after, we end up with no default grub :(

usr/lib/live-installer/installer.py

@@ -123,8 +123,8 @@ def start_installation(self):
  os.system("cp /run/live/medium/pool/main/g/grub2/grub-efi* /target/debs/")
  os.system("cp /run/live/medium/pool/main/g/grub-efi-amd64-signed/* /target/debs/")
  os.system("cp /run/live/medium/pool/main/s/shim*/* /target/debs/")
- self.do_run_in_chroot("dpkg -i /debs/*")
  self.do_run_in_chroot("DEBIAN_FRONTEND=noninteractive apt-get remove --purge --yes grub-pc")
+ self.do_run_in_chroot("dpkg -i /debs/*")
  os.system("rm -rf /target/debs")
 
  print(" --> Installing microcode packages")