Move DocData and Collada out of their subfolders

Now that the unused DocDump was removed, the `editor/doc` subfolder is
redundant.

Similarly, there's no reason for Collada to have a subfolder for itself
when glTF or OBJ don't.

editor/doc/SCsub

@@ -1,5 +0,0 @@
-#!/usr/bin/env python
-
-Import('env')
-
-env.add_source_files(env.editor_sources, "*.cpp")