pkg/grub: remove old patch folders superseded by patches-2.12

Drop patches/, patches-2.06/, patches-aarch64-2.06/, and
patches-riscv64-2.06/ — all absorbed into the new unified
patches-2.12/ set in the previous commit.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Mikhail Malyshev <mike.malyshev@gmail.com>

Author: rucoder