Undo the string_view patch (#257)

Author: an-tao

trantor/utils/LogStream.h

@@ -22,10 +22,6 @@
 #include <string.h>  // memcpy
 #include <string>
 
-#if __cplusplus >= 201703L || (defined(_MSVC_LANG) && _MSVC_LANG >= 201703L)
-#include <string_view>
-#endif
-
 namespace trantor
 {
 namespace detail
@@ -204,13 +200,6 @@ class TRANTOR_EXPORT LogStream : NonCopyable
         append(v.c_str(), v.size());
         return *this;
     }
-#if __cplusplus >= 201703L || (defined(_MSVC_LANG) && _MSVC_LANG >= 201703L)
-    self &operator<<(const std::string_view v)
-    {
-        append(v.data(), v.length());
-        return *this;
-    }
-#endif
 
     void append(const char *data, size_t len)
     {