swift234

remove some unnecessary code that produces unfortunate effects when other changes go in.
The fallthrough path that this enables does ambiguity checking and simplifies active 
constraints that are left into the system, before jumping into diagnoseFailureForExpr.
By jumping into diagnoseFailureForExpr directly, CSDiags can produce the wrong
diagnostic because the constraints are still on the active list.

NFC for now because other changes are needed to provoke this.



Swift SVN r31272