newsprint: remove erronous double-description to fix leak
description() is defined as: pspec->_blurb = g_strdup (blurb);
Using description() twice for a given property will result in the first description being lost and leaked - we therefore remove one description to both fix the leak and ensure that the property is using the right description.
The second description looks like it was copied from the "Black angle" declaration below, and has existed since "Black period" was first added in: 5113e8e3 (newsprint: add custom period to each colorant, 2019-07-17)