[ticket/13019] Always accept a reason for deleting a post/topic.

PHPBB3-13019
[ticket/13019] Rename deletion reason label.

PHPBB3-13019
[ticket/13019] Do not hide reason field when deleting permanently.

PHPBB3-13019
Merge pull request #2956 from prototech/ticket/13019

[ticket/13019] Always accept a reason for deleting a post/topic.

* prototech/ticket/13019:
  [ticket/13019] Do not hide reason field when deleting permanently.
  [ticket/13019] Rename deletion reason label.
  [ticket/13019] Always accept a reason for deleting a post/topic.