[-Wunused-private-field] (clang) - remove

In file included from gnucash/gnome-utils/dialog-options.cpp:34:
gnucash/gnome-utils/dialog-options.hpp:55:10: warning: private field 'toplevel' is not used [-Wunused-private-field]
    bool toplevel;
         ^

In file included from gnucash/import-export/csv-imp/gnc-imp-props-price.cpp:42:
gnucash/import-export/csv-imp/gnc-imp-props-price.hpp:113:10: warning: private field 'created' is not used [-Wunused-private-field]
    bool created = false;
         ^

libgnucash/backend/dbi/gnc-dbisqlconnection.cpp:53:29: warning: private field 'm_conn' is not used [-Wunused-private-field]
    const GncSqlConnection* m_conn = nullptr;
                            ^
libgnucash/backend/sql/test/utest-gnc-backend-sql.cpp:81:33: warning: private field 'm_conn' is not used [-Wunused-private-field]
    const GncMockSqlConnection* m_conn;
                                ^

gnucash/gnome-utils/dialog-options.hpp

@@ -52,8 +52,6 @@ class GncOptionsDialog
     GtkButton  * m_apply_button;
     GtkButton  * m_ok_button;
 
-    bool toplevel;
-
     GncOptionsDialogCallback m_apply_cb;
     gpointer             m_apply_cb_data;
 

gnucash/import-export/csv-imp/gnc-imp-props-price.hpp

@@ -110,7 +110,6 @@ private:
     std::optional<std::string> m_from_namespace;
     std::optional<std::string> m_from_symbol;
     std::optional<gnc_commodity*> m_to_currency;
-    bool created = false;
 
     std::map<GncPricePropType, std::string> m_errors;
 };

libgnucash/backend/dbi/gnc-dbisqlconnection.cpp

@@ -43,14 +43,13 @@ const std::string lock_table = "gnclock";
 class GncDbiSqlStatement : public GncSqlStatement
 {
 public:
-    GncDbiSqlStatement(const GncSqlConnection* conn, const std::string& sql) :
-        m_conn{conn}, m_sql {sql} {}
+    GncDbiSqlStatement(const std::string& sql) :
+        m_sql {sql} {}
     ~GncDbiSqlStatement() {}
     const char* to_sql() const override;
     void add_where_cond(QofIdTypeConst, const PairVec&) override;
 
 private:
-    const GncSqlConnection* m_conn = nullptr;
     std::string m_sql;
 };
 
@@ -321,7 +320,7 @@ GncSqlStatementPtr
 GncDbiSqlConnection::create_statement_from_sql (const std::string& sql)
     const noexcept
 {
-    return std::unique_ptr<GncSqlStatement>{new GncDbiSqlStatement (this, sql)};
+    return std::unique_ptr<GncSqlStatement>{new GncDbiSqlStatement (sql)};
 }
 
 bool

libgnucash/backend/sql/test/utest-gnc-backend-sql.cpp

@@ -48,8 +48,8 @@ class GncMockSqlConnection;
 class GncMockSqlResult : public GncSqlResult
 {
 public:
-    GncMockSqlResult(const GncMockSqlConnection* conn) :
-        m_conn{conn}, m_iter{this}, m_row{&m_iter} {}
+    GncMockSqlResult() :
+        m_iter{this}, m_row{&m_iter} {}
     uint64_t size() const noexcept { return 1; }
     GncSqlRow& begin() { return m_row; }
     GncSqlRow& end() { return m_row; }
@@ -78,7 +78,6 @@ protected:
             GncMockSqlResult* m_inst;
         };
 private:
-    const GncMockSqlConnection* m_conn;
     IteratorImpl m_iter;
     GncSqlRow m_row;
 };
@@ -94,7 +93,6 @@ public:
 class GncMockSqlConnection : public GncSqlConnection
 {
 public:
-    GncMockSqlConnection() : m_result{this} {}
     GncSqlResultPtr execute_select_statement (const GncSqlStatementPtr&)
         noexcept override { return &m_result; }
     int execute_nonselect_statement (const GncSqlStatementPtr&)