[SIL Optimizer] Remove now-unused static function. NFC

Author: DougGregor

lib/SILOptimizer/Utils/Local.cpp

@@ -1332,28 +1332,6 @@ void ValueLifetimeAnalysis::dump() const {
 //                    Casts Optimization and Simplification
 //===----------------------------------------------------------------------===//
 
-/// \brief Get a substitution corresponding to the type witness.
-/// Inspired by ProtocolConformance::getTypeWitnessByName.
-static const Substitution *
-getTypeWitnessByName(ProtocolConformance *conformance, Identifier name) {
-  // Find the named requirement.
-  AssociatedTypeDecl *assocType = nullptr;
-  assert(conformance && "Missing conformance information");
-  auto members = conformance->getProtocol()->lookupDirect(name);
-  for (auto member : members) {
-    assocType = dyn_cast<AssociatedTypeDecl>(member);
-    if (assocType)
-      break;
-  }
-
-  if (!assocType)
-    return nullptr;
-
-  if (!conformance->hasTypeWitness(assocType, nullptr)) {
-    return nullptr;
-  }
-  return &conformance->getTypeWitness(assocType, nullptr);
-}
 
 /// Check if is a bridging cast, i.e. one of the sides is
 /// a bridged type.