test/*.cc: use '= default'

created with clang-tidy --fix --checks=-*,modernize-use-equals-default

Change-Id: I706044a9f442ef39c07b03f562c36c7db86721b1
diff --git a/test/avg_test.cc b/test/avg_test.cc
index 4cf22f6..bbbb420 100644
--- a/test/avg_test.cc
+++ b/test/avg_test.cc
@@ -582,8 +582,8 @@
 class VectorVarTestBase : public ::testing::Test {
  public:
   explicit VectorVarTestBase(int bwl) { m_bwl = bwl; }
-  VectorVarTestBase() {}
-  ~VectorVarTestBase() override {}
+  VectorVarTestBase() = default;
+  ~VectorVarTestBase() override = default;
 
  protected:
   static const int kDataAlignment = 16;