Remove grub2 sections workaround

In past modified section is used to pass changes in kernel parameters,
but with new yast2-bootloader API it is no longer needed and it can
cause unexped results ( like if more sections is modified or missing
xen_append modification ).
remove also from grub2efi workaround
Merge pull request #38 from openSUSE/remove_workaround

Remove grub2 sections workaround