Debian: Revert compatibility=grub2

This doesn't work on Debian Bullseye.  While I tested the actual
create command on unstable, I know I looked at a file list on
packages.debian.org.  I must have looked at bullseye-backports by
mistake.  That's what I get for not testing the whole thing!

This partially reverts commit 7343c2253f.

Reported-by: anarcat
Closes #309
Signed-off-by: Richard Laager <rlaager@wiktel.com>

docs/Getting Started/Debian/Debian Bullseye Root on ZFS.rst

@@ -227,9 +227,19 @@ Step 2: Disk Formatting
 
      zpool create \
          -o cachefile=/etc/zfs/zpool.cache \
-         -o ashift=12 -o autotrim=on \
-         -o compatibility=grub2 \
+         -o ashift=12 -o autotrim=on -d \
+         -o feature@async_destroy=enabled \
+         -o feature@bookmarks=enabled \
+         -o feature@embedded_data=enabled \
+         -o feature@empty_bpobj=enabled \
+         -o feature@enabled_txg=enabled \
+         -o feature@extensible_dataset=enabled \
+         -o feature@filesystem_limits=enabled \
+         -o feature@hole_birth=enabled \
+         -o feature@large_blocks=enabled \
          -o feature@livelist=enabled \
+         -o feature@lz4_compress=enabled \
+         -o feature@spacemap_histogram=enabled \
          -o feature@zpool_checkpoint=enabled \
          -O acltype=posixacl -O canmount=off -O compression=lz4 \
          -O devices=off -O normalization=formD -O relatime=on -O xattr=sa \
@@ -238,9 +248,6 @@ Step 2: Disk Formatting
 
    You should not need to customize any of the options for the boot pool.
 
-   Ignore the warnings about the features “not in specified 'compatibility'
-   feature set.”
-
    GRUB does not support all of the zpool features. See ``spa_feature_names``
    in `grub-core/fs/zfs/zfs.c
    <http://git.savannah.gnu.org/cgit/grub.git/tree/grub-core/fs/zfs/zfs.c#n276>`__.