Moves by banks to ditch law firms snared in the “robo-signing” mess are spreading delays and confusion to borrowers, while angering judges grappling with thousands of foreclosure cases now trapped in limbo. The trouble began when U.S. banks and government-owned mortgage giants lost confidence in some law firms that handled a huge volume of foreclosures. After controversy erupted last fall over the shoddy review of loan documents known as robo-signing, banks dropped some law firms.