MokManager: calculate the variable size correctly

MokSize of the hash signature list includes the owner GUID,
so we should not add the 16bytes compensation.

Signed-off-by: Gary Ching-Pang Lin <glin@suse.com>
MokManager: fix the hash list counting in delete

match_hash() requests the number of keys in a list and it was
mistakenly replaced with the size of the Mok node. This would
made MokManager to remove the whole Mok node instead of one
hash.

Signed-off-by: Gary Ching-Pang Lin <glin@suse.com>