remove unused var (#2006)

Signed-off-by: xudl <isxudl@163.com>

Co-authored-by: xudl <isxudl@163.com>

core/src/utils/LogUtil.cpp

@@ -41,7 +41,6 @@ RolloutHandler(const char* filename, std::size_t size, el::Level level) {
     char* base = basename(basec);
 
     std::string s(base);
-    std::stringstream ss;
     std::string list[] = {"\\", " ", "\'", "\"", "*", "\?", "{", "}", ";", "<",
                           ">",  "|", "^",  "&",  "$", "#",  "!", "`", "~"};
     std::string::size_type position;