Remove unused local variables

[ma8ma]

未使用の変数が存在するとcppcheckに指摘されたため削除します。

cppcheckのレポート

src/article/embeddedimage.cpp:135:17: style: Unused variable: errmsg [unusedVariable]
    std::string errmsg;
                ^
src/config/configitems.cpp:485:30: style: Unused variable: list_tmp [unusedVariable]
    std::list< std::string > list_tmp;
                             ^
src/config/configitems.cpp:486:40: style: Unused variable: it_tmp [unusedVariable]
    std::list< std::string >::iterator it_tmp;
                                       ^
src/bbslist/bbslistviewbase.cpp:3004:32: style: Unused variable: list_path [unusedVariable]
    std::list< Gtk::TreePath > list_path;
                               ^
src/dbimg/img.cpp:780:34: style: Unused variable: list_tmp [unusedVariable]
        std::list< std::string > list_tmp;
                                 ^
src/dbimg/img.cpp:781:44: style: Unused variable: it_tmp [unusedVariable]
        std::list< std::string >::iterator it_tmp;
                                           ^
src/globalabonethreadpref.h:65:25: style: Unused variable: str_name [unusedVariable]
            std::string str_name, str_word, str_regex;
                        ^