ufs: ufs_sb_private_info: remove unused s_{2,3}apb fields

ufs: ufs_sb_private_info: remove unused s_{2,3}apb fields

These two fields are populated and stored as a "frequently used value"
in ufs_fill_super, but are not used afterwards in the driver.

Moreover, one of the shifts triggers UBSAN: shift-out-of-bounds when
apbshift is 12 because 12 * 3 = 36 and 1 << 36 does not fit in the 32
bit integer used to store the value.

Closes: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2087853
Signed-off-by: Agathe Porte <agathe.porte@canonical.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>