Planepix.txt no longer used in the plane-alert-db repo

[dziban303]

As mentioned in discord, apparently planepix.txt has been moved to a subfolder, https://github.com/sdr-enthusiasts/plane-alert-db/raw/main/_bin/planepix.txt. It seems that the file's role has been replaced with plane_images.txt which is concatenated with other files to produce the *-images.csv files.

During startup or on config change it looks like planepix.txt is supposed to be downloaded into planepix.txt.samplefile in the user's persistent storage. Since it's not there anymore, planepix.txt.samplefile is instead filled with the '404' error.

I'm not sure it's worth fixing; at 630KB, it's kind of big for a sample.

The other mentions of planepix.txt in the code show that it would be used to download an image if a screenshot failed. That wouldn't work anyway by default as the planepix.txt file doesn't exist unless the user creates it or renames the sample file, so it seems like an edge case.

Anyway, issue reported.