[ConstraintSystem] Stop using CheckedConformances cache

It was necessary only for `applySolutionToForEachStmt` in `CSApply`,
diagnostic can avoid it and use information stored in the locator
instead.

Author: xedin

lib/Sema/CSApply.cpp

@@ -7972,12 +7972,8 @@ static Optional<SolutionApplicationTarget> applySolutionToForEachStmt(
   auto stmt = forEachStmtInfo.stmt;
   auto sequenceProto = TypeChecker::getProtocol(
       cs.getASTContext(), stmt->getForLoc(), KnownProtocolKind::Sequence);
-  auto contextualLocator = solution.getConstraintLocator(
-      target.getAsExpr(),
-      {LocatorPathElt::ContextualType(),
-       LocatorPathElt::ConformanceRequirement(sequenceProto)});
-  auto sequenceConformance =
-      solution.resolveConformance(contextualLocator, sequenceProto);
+  auto sequenceConformance = TypeChecker::conformsToProtocol(
+      forEachStmtInfo.sequenceType, sequenceProto, cs.DC);
   assert(!sequenceConformance.isInvalid() &&
          "Couldn't find sequence conformance");
 

lib/Sema/CSSimplify.cpp

@@ -5721,18 +5721,17 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyConformsToConstraint(
   /// Record the given conformance as the result, adding any conditional
   /// requirements if necessary.
   auto recordConformance = [&](ProtocolConformanceRef conformance) {
-    auto *conformanceLoc = getConstraintLocator(
-        loc, LocatorPathElt::ConformanceRequirement(protocol));
-    // Record the conformance.
-    CheckedConformances.push_back({conformanceLoc, conformance});
-
-    if (isConformanceUnavailable(conformance, conformanceLoc))
+    if (isConformanceUnavailable(conformance, loc))
       increaseScore(SK_Unavailable);
 
     // This conformance may be conditional, in which case we need to consider
     // those requirements as constraints too.
     if (conformance.isConcrete()) {
       unsigned index = 0;
+      auto *conformanceLoc = getConstraintLocator(
+          loc,
+          LocatorPathElt::ConformanceRequirement(conformance.getConcrete()));
+
       for (const auto &req : conformance.getConditionalRequirements()) {
         addConstraint(
             req, getConstraintLocator(conformanceLoc,