add inst/pbfs to .Rbuildignore

[JosiahParry]

The pbfs are bloating the installation size of the package from 2.5mb to 8-11mb depending on the OS. This is unneeded.

[JosiahParry]

Specifically, the big-polys needs to be removed

[JosiahParry]

Also remove the json from the installed package big-pnts.json