Remove explicit calls to computeRequirementSignature

We can rely on lazy calls to getRequirementSignature instead.

lib/ClangImporter/ImportDecl.cpp

@@ -4521,10 +4521,6 @@ namespace {
                           inheritedTypes);
       result->setInherited(Impl.SwiftContext.AllocateCopy(inheritedTypes));
 
-      // Compute the requirement signature.
-      if (!result->isRequirementSignatureComputed())
-        result->computeRequirementSignature();
-
       result->setMemberLoader(&Impl, 0);
 
       // Add the protocol decl to ExternalDefinitions so that IRGen can emit
@@ -7878,9 +7874,6 @@ void ClangImporter::Implementation::finishNormalConformance(
   PrettyStackTraceConformance trace(SwiftContext, "completing import of",
                                     conformance);
 
-  if (!proto->isRequirementSignatureComputed())
-    proto->computeRequirementSignature();
-
   finishTypeWitnesses(conformance);
   finishInheritedConformances(conformance);
   finishSignatureConformances(conformance);