It makes little sense to centralise the definitions for things like
Steam, GoG, etc.. These paths are only useful in the case where the user
has derived the data from such a store, has installed ioq3 in a separate
location, and we want it do be able to find said data. If a derivative
project has deployed (binaries and all) on e.g. Steam then for them
fs_basepath will already be correct, and fs_steampath is not useful.
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