impl Drop for Appender has unnecessary unsafe calls.

[era127]

According to the C appender api documentation, the drop of appender should only need to call duckdb_appender_destroy. I believe the flush and duckdb_appender_close call can be removed.

impl Drop for Appender<'_> {
    fn drop(&mut self) {
        if !self.app.is_null() {
  // remove     self.flush();
            unsafe {
  // remove     ffi::duckdb_appender_close(self.app);
                ffi::duckdb_appender_destroy(&mut self.app);
            }
        }
    }
}