_setup_assoc_cond_limits was using the table 'prefix' passed by argument
in the where clause to select the where clause prefix.deleted=something.

It turns out that _setup_assoc_cond_limits is called by these functions:
as_mysql_modify_assocs
as_mysql_remove_assocs
as_mysql_get_assocs
as_mysql_acct_no_users

which set the prefix to 't2' before the call if a QOS is provided or if
WithSubAccounts is provided. The 't2' prefix is fine for other where
conditions in that case, but for choosing the deleted we need the t1
which is the table we're selecting the records off.

Bug 3835