jqueue: Remove lock status field

With the job queue changes for Ganeti 2.2, watched and queried jobs are
loaded directly from disk, rendering the in-memory “lock_status” field
useless. Writing it to disk would be possible, but has a huge cost at
runtime (when tested, processing 1'000 opcodes involved 4'000 additional
writes to job files, even with replication turned off).

Using an additional in-memory dictionary to just manage this field turned
out to be a complicated task due to the necessary locking.

The plan is to introduce a more generic lock debugging mechanism in the
near future. Hence the decision is to remove this field now instead of
spending a lot of time to make it working again.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>