Remove WHERE clause when selecting all tags

The `tags` table doesn't have a `deleted` column ([schema](https://github.com/etsy/morgue/blob/master/schemas/morgue.sql#L26)).

As mentioned in #8, when trying to fetch all of the tags a sql exception is thrown:
```
SQLSTATE[42S22]: Column not found: 1054 Unknown column 'deleted' in 'where clause'
````

Instead of removing the WHERE clause entirely I could change this to a `JOIN` with the [`postmortem_referenced_tags `](https://github.com/etsy/morgue/blob/master/schemas/morgue.sql#L32) table to only show tags that are being used. Let me know and I can update the PR.