grub: strip quiet even if splash is not there

Ubuntu always sets "quiet splash", but Debian usually may come with just
"quiet". There is no reason to always match for both, so adapt our
sed/grep regexpes accordingly.

While at it, remove the grub1 stanza, as we have no grub1 anywhere in
our infrastructure anymore.

Change-Id: I2b21bb6d677a8cb14c9d045c9d1096b7f358cdd6