Consolidate has_data and has_data_v

There are two separate implementations for `has_data` and `has_data_v` that do the same thing. This change combines those implementations.

btas/tensor_traits.h

@@ -9,20 +9,6 @@
 
 namespace btas {
 
-/// test T has data() member
-/// this will be used to detect whether or not the storage is consecutive
-template<class T>
-class has_data {
-   /// true case
-   template<class U>
-   static auto __test(U* p) -> decltype(p->data(), std::true_type());
-   /// false case
-   template<class>
-   static std::false_type __test(...);
-public:
-   static constexpr const bool value = std::is_same<std::true_type, decltype(__test<T>(0))>::value;
-};
-
 /// test T has range_type
 template<class T>
 class has_range_type {

btas/type_traits.h

@@ -125,10 +125,22 @@ namespace btas {
   template <typename T>
   constexpr inline bool has_squarebraket_v = has_squarebraket<T>::value;
 
-  template <typename S, typename Enabler = void>
-  constexpr static bool has_data_v = false;
-  template <typename S>
-  constexpr static bool has_data_v<S, std::void_t<decltype(std::declval<S&>().data())>> = true;
+  /// test T has data() member
+  /// this will be used to detect whether or not the storage is consecutive
+  template<class T>
+  class has_data {
+    /// true case
+    template<class U>
+    static auto __test(U* p) -> decltype(p->data(), std::true_type());
+    /// false case
+    template<class>
+    static std::false_type __test(...);
+  public:
+    static constexpr const bool value = std::is_same<std::true_type, decltype(__test<T>(0))>::value;
+  };
+
+  template <typename T>
+  inline constexpr bool has_data_v = has_data<T>::value;
 
   template <typename S, typename Enabler = void>
   constexpr static bool has_size_v = false;