mlxsw: Revert "Prepare for XM implementation - prefix insertion and removal"

This reverts commit e7086213 ("Merge branch
'mlxsw-spectrum-prepare-for-xm-implementation-prefix-insertion-and-removal'").

Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>