Remove the TII::scheduleTwoAddrSource() hook.

It never does anything when running 'make check', and it get's in the
way of updating live intervals in 2-addr.

The hook was originally added to help form IT blocks in Thumb2 code
before register allocation, but the pass ordering has changed since
then, and we run if-conversion after register allocation now.

When the MI scheduler is enabled, there will be no less than two
schedulers between 2-addr and Thumb2ITBlockPass, so this hook is
unlikely to help anything.

llvm-svn: 161794