Remove context from plot in module docstring
Remove context from plot in module docstring

The plot from another module (gravmag.eqlayer) was being inserted
as well.

victortxa/fatiando,drandykass/fatiando,cmeessen/fatiando,mtb-za/fatiando,santis19/fatiando,rafaelmds/fatiando,drandykass/fatiando,rafaelmds/fatiando,fatiando/fatiando,fatiando/fatiando,victortxa/fatiando,cmeessen/fatiando,santis19/fatiando,mtb-za/fatiando