[ticket/12778] Automatically delete files on update

PHPBB3-12778
[ticket/12778] Rename the file to *.bak instead of deleting

PHPBB3-12778
Merge pull request #2815 from dhruvgoel92/ticket/12778

[ticket/12778] Automatically delete files on update

* dhruvgoel92/ticket/12778:
  [ticket/12778] Rename the file to *.bak instead of deleting
  [ticket/12778] Automatically delete files on update