[IMP] base: remove sql view that prevents column changings

Small fix for error (similar to #159):

```
2014-12-12 09:22:42,129 23335 ERROR testdb openerp.sql_db: bad query: ALTER TABLE "ir_attachment" ALTER COLUMN "datas_fname" TYPE VARCHAR
Traceback (most recent call last):
  File "/var/tmp/openupgrade/8.0/server/openerp/sql_db.py", line 234, in execute
    res = self._obj.execute(query, params)
NotSupportedError: cannot alter type of a column used by a view or rule
DETAIL:  rule _RETURN on view report_document_user depends on column "datas_fname"
```