lsblk: don't duplicate columns

lsblk: don't duplicate columns

$ lsblk --discard --perms
NAME   DISC-ALN DISC-GRAN DISC-MAX DISC-ZERO NAME     SIZE OWNER GROUP MODE
sdb           0        0B       0B         0 sdb     74.5G root  disk  brw-rw----
└─sdb1        0        0B       0B         0 └─sdb1  74.5G root  disk  brw-rw----
sda           0      512B       2G         0 sda    223.6G root  disk  brw-rw----
├─sda4        0      512B       2G         0 ├─sda4    50G root  disk  brw-rw----
├─sda2        0      512B       2G         0 ├─sda2   200M root  disk  brw-rw----
├─sda5        0      512B       2G         0 ├─sda5  35.1G root  disk  brw-rw----
├─sda3        0      512B       2G         0 ├─sda3 130.3G root  disk  brw-rw----
├─sda1        0      512B       2G         0 ├─sda1   200M root  disk  brw-rw----
└─sda6        0      512B       2G         0 └─sda6   7.8G root  disk  brw-rw----

... see NAME column.

It's fine to support duplicated columns when requested by user (e.g.
-o NAME,NAME,SIZE), but it does not make sense for the default output
when multiple command options specified.

Signed-off-by: Karel Zak <kzak@redhat.com>