[CSOptimizer] Remove an outdated optimization to compare resolved argument types with all else equal

This is already accounted for by `determineBestChoicesInContext`
and reflected in the overall score, which means that we no longer
need to use this in vacuum.

Author: xedin

include/swift/Sema/Constraint.h

@@ -825,11 +825,6 @@ class Constraint final : public llvm::ilist_node<Constraint>,
     });
   }
 
-  /// Returns the number of resolved argument types for an applied disjunction
-  /// constraint. This is always zero for disjunctions that do not represent
-  /// an applied overload.
-  unsigned countResolvedArgumentTypes(ConstraintSystem &cs) const;
-
   /// Determine if this constraint represents explicit conversion,
   /// e.g. coercion constraint "as X" which forms a disjunction.
   bool isExplicitConversion() const;

lib/Sema/CSOptimizer.cpp

@@ -662,16 +662,9 @@ ConstraintSystem::selectDisjunction() {
         unsigned firstFavored = favorings[first].size();
         unsigned secondFavored = favorings[second].size();
 
-        // Everything else equal, choose the disjunction with the greatest
-        // number of resolved argument types. The number of resolved argument
-        // types is always zero for disjunctions that don't represent applied
-        // overloads.
         if (firstFavored == secondFavored) {
           if (firstActive != secondActive)
             return firstActive < secondActive;
-
-          return first->countResolvedArgumentTypes(*this) >
-                 second->countResolvedArgumentTypes(*this);
         }
 
         firstFavored = firstFavored ? firstFavored : firstActive;

lib/Sema/Constraint.cpp

@@ -711,17 +711,6 @@ gatherReferencedTypeVars(Constraint *constraint,
   }
 }
 
-unsigned Constraint::countResolvedArgumentTypes(ConstraintSystem &cs) const {
-  auto *argumentFuncType = cs.getAppliedDisjunctionArgumentFunction(this);
-  if (!argumentFuncType)
-    return 0;
-
-  return llvm::count_if(argumentFuncType->getParams(), [&](const AnyFunctionType::Param arg) {
-    auto argType = cs.getFixedTypeRecursive(arg.getPlainType(), /*wantRValue=*/true);
-    return !argType->isTypeVariableOrMember();
-  });
-}
-
 bool Constraint::isExplicitConversion() const {
   assert(Kind == ConstraintKind::Disjunction);