libparted: remove _loop_get_partition_range

libparted: remove _loop_get_partition_range

Commit 1eb0cc30 added support for loop devices to be partitioned,
but it only enabled that support if the kernel parameter max_part
was non zero.  This parameter just reserves minor numbers for
partitions in the traditional sequence that hard disks used.
When it is zero, it is still possible to add partitions, they
just will get minor numbers from another pool.  Removing this
check allows partitions to be used on loop devices even when the
loop module was not loaded with the max_part argument.
* libparted/arch/linux.c (_loop_get_partition_range): Remove function
and all uses.