They are not particularly packaged in Linux distros so we do not facilitate unbundling via SCons. There could be done if/when there is interest. Also s/pnm/pbm/, long-lived typo :) (cherry picked from commit b1e8889d96)
b1e8889d96
Also removes a couple wrong Godot headers from third-party source files.
-Removed support of loading BitMap as image, now it must be load as a pnm, also closes #2040