You would think that a bank with a small presence in mortgages would jump at the opportunity to keep the fast-growing residential arm of a merger partner. But that’s not the case with MF Financial, a mid-sized bank that earlier in the week announced that it would buy Taylor Capital, parent of Cole Taylor Bank, in a stock deal valued at $680 million. Although MF Financial took a close look at the subsidiary, Cole Taylor Mortgage, it decided that the unit is not essential to the deal. In fact, it’s so non-essential ...