Use `inline` on all namespace-scope constants defined in headers

Change-Id: Ia6e68d3fe572f6c15978c77a646ac599fa47e575
diff --git a/tests/unit/security/validator-fixture.cpp b/tests/unit/security/validator-fixture.cpp
index 8579fc8..0e780b4 100644
--- a/tests/unit/security/validator-fixture.cpp
+++ b/tests/unit/security/validator-fixture.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2022 Regents of the University of California.
+ * Copyright (c) 2013-2023 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -28,9 +28,6 @@
 inline namespace v2 {
 namespace tests {
 
-const time::milliseconds ValidatorFixtureBase::s_mockPeriod{250};
-const int ValidatorFixtureBase::s_mockTimes = 200;
-
 ValidatorFixtureBase::ValidatorFixtureBase()
 {
   processInterest = [this] (const Interest& interest) {