[SILGen] Eliminate useConformancesFromSubstitutions() on SubstitutionList.

Update one caller first.

Author: DougGregor

lib/SILGen/SILGen.cpp

@@ -1383,14 +1383,6 @@ void SILGenModule::useConformance(ProtocolConformanceRef conformanceRef) {
   usedConformances.insert(root);
 }
 
-void
-SILGenModule::useConformancesFromSubstitutions(SubstitutionList subs) {
-  for (auto &sub : subs) {
-    for (auto conformance : sub.getConformances())
-      useConformance(conformance);
-  }
-}
-
 void SILGenModule::useConformancesFromSubstitutions(
                                                 const SubstitutionMap subs) {
   for (auto conf : subs.getConformances())

lib/SILGen/SILGen.h

@@ -425,9 +425,6 @@ class LLVM_LIBRARY_VISIBILITY SILGenModule : public ASTVisitor<SILGenModule> {
   /// it's in our TU.
   void useConformance(ProtocolConformanceRef conformance);
 
-  /// Mark protocol conformances from the given set of substitutions as used.
-  void useConformancesFromSubstitutions(SubstitutionList subs);
-
   /// Mark protocol conformances from the given set of substitutions as used.
   void useConformancesFromSubstitutions(SubstitutionMap subs);
 

lib/SILGen/SILGenBuilder.cpp

@@ -77,8 +77,7 @@ MetatypeInst *SILGenBuilder::createMetatype(SILLocation loc, SILType metatype) {
       auto subMap = t->getContextSubstitutionMap(getSILGenModule().SwiftModule,
                                                  decl);
       SmallVector<Substitution, 4> subs;
-      genericSig->getSubstitutions(subMap, subs);
-      getSILGenModule().useConformancesFromSubstitutions(subs);
+      getSILGenModule().useConformancesFromSubstitutions(subMap);
       return false;
     });