Update allow partition deletion comment in set_valid_operations()

This previous commit [1] suggested that in future partition deletion
might be allowed even while a LUKS mapping was active in that partition.
To allow deletion of a partition while it has active content is wrong.
That is a significant reason GParted has busy detection of otherwise
unrecognised file systems [2] and recognition and busy detection of, but
otherwise not controllable support for, Linux Software RAID [3] and
ATARAID [4][5] arrays.

To automatically close the LUKS partition first would be against the
pattern of behaviour that GParted has established, of requiring explicit
deactivation of file systems, swap and volume groups before allowing
deletion.  Therefore update the comment accordingly.

[1] f1e3d42b56
    Prevent deletion of open LUKS mappings (#774818)

[2] 49a2e19462
    Restore busy detection of unknown mounted file systems (#723842)

[3] d2e1130ad2
    Detect busy status of Linux Software RAID members (#709640)

[4] 6e990ea48a
    Detect busy status of mdadm started ATARAID members (#75)

[5] caec22871e
    Detect busy status of dmraid started ATARAID members (#75)

src/Win_GParted.cc

@@ -1392,8 +1392,7 @@ void Win_GParted::set_valid_operations()
 	{
 		allow_format( true ) ;
 
-		// only allow deletion of partitions within a partition table
-		// Also exclude open LUKS mappings until open/close is supported
+		// Only allow deletion of inactive partitions within a partition table.
 		if ( ( selected_partition_ptr->type == TYPE_PRIMARY ||
 		       selected_partition_ptr->type == TYPE_LOGICAL    ) &&
 		     ! selected_partition_ptr->busy                         )