fix: template knot quality: count all pixels for Nko

[hlruh]

Remove indexing ind of valid pixels in counting of pixels per template knot. The valid pixels are selected by the bmod==0 condition already. For the counting of all possible pixels contributing to a knot (Nko), the all the pixels have to be counted not only valid pixels.

[mzechmeister]

When dropping ind, then the histogram argument weights can be omitted completely, since all weights are one: https://github.com/mzechmeister/serval/blob/79826e1d1c552806d7832a391131c1f7cae25f9f/src/serval.py#L1835