remove legacy test for None log message
remove legacy test for None log message

Writing `None` to the log was used to flush context information to the logs.
The functionality to display progress information, including rate limiting, has
been incoporated inside the log objects (see 72fea624, 0a96e17d).

joostvanzwieten/nutils,CVerhoosel/nutils,nutils/nutils,wijnandhoitinga/nutils