interest: remove deprecated setDefaultCanBePrefix()

Change-Id: Ifaffb7cc7772a31c3b396c60b816e783d70b7041
diff --git a/tests/unit/security/validation-policy-signed-interest.t.cpp b/tests/unit/security/validation-policy-signed-interest.t.cpp
index d9cddb5..c3d37e6 100644
--- a/tests/unit/security/validation-policy-signed-interest.t.cpp
+++ b/tests/unit/security/validation-policy-signed-interest.t.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2020 Regents of the University of California.
+ * Copyright (c) 2013-2022 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -75,7 +75,6 @@
                      uint32_t signingFlags = InterestSigner::WantNonce | InterestSigner::WantTime)
   {
     Interest i(Name(identity.getName()).append("CMD"));
-    i.setCanBePrefix(false);
     m_signer.makeSignedInterest(i, signingByIdentity(identity), signingFlags);
     return i;
   }
@@ -102,7 +101,6 @@
   VALIDATE_SUCCESS(i2, "Should succeed (timestamp and sequence number larger than previous)");
 
   Interest i3(Name(identity.getName()).append("CMD"));
-  i3.setCanBePrefix(false);
   m_signer.makeSignedInterest(i3, signingWithSha256());
   VALIDATE_FAILURE(i3, "Should fail (Sha256 signature violates policy)");
 }