[CSGen] Remove redundant r-value adjustment constraint

Since unresolved members now introduce an implicit expression
during pre-check, there is no need to add a separate r-value
adjustment constraint to connect "tail" of the chain with
chain result.

Author: xedin

lib/Sema/CSGen.cpp

@@ -1446,9 +1446,6 @@ namespace {
 
       // The result of the last element of the chain must be convertible to the
       // whole chain, and the type of the whole chain must be equal to the base.
-      CS.addConstraint(
-          ConstraintKind::Conversion, memberTy, chainBaseTy,
-          CS.getConstraintLocator(tail, ConstraintLocator::RValueAdjustment));
       CS.addConstraint(ConstraintKind::Conversion, memberTy, chainResultTy,
                        locator);
       CS.addConstraint(ConstraintKind::Equal, chainBaseTy, chainResultTy,