Fix _drop_unique_constraint_in_sqlite() function.

We got incorrect unique constrains in function
_drop_unique_constraint_in_sqlite().
New function `_get_unique_constraints_in_sqlite()` was added to fix it.

Change-Id: Iebb4c0e6c3e6a069ba5cde2fdb2a2ff1200b826f
Fixes: bug 1184526
Merge "Fix _drop_unique_constraint_in_sqlite() function."