Removing Blender Game Engine from Blender 2.8

Folders removed entirely:
* //extern/recastnavigation
* //intern/decklink
* //intern/moto
* //source/blender/editors/space_logic
* //source/blenderplayer
* //source/gameengine

This includes DNA data and any reference to the BGE code in Blender itself.
We are bumping the subversion.

Pending tasks:
* Tile/clamp code in image editor draw code.
* Viewport drawing code (so much of this will go away because of BI removal
  that we can wait until then to remove this.

source/blender/python/generic/bpy_internal_import.h

@@ -51,12 +51,7 @@ PyObject   *bpy_text_reimport(PyObject *module, int *found);
 
 void bpy_text_filename_get(char *fn, size_t fn_len, struct Text *text);
 
-/* The game engine has its own Main struct, if this is set search this rather than G.main */
 struct Main *bpy_import_main_get(void);
 void bpy_import_main_set(struct Main *maggie);
 
-/* This is used for importing text from dynamically loaded libraries in the game engine */
-void bpy_import_main_extra_add(struct Main *maggie);
-void bpy_import_main_extra_remove(struct Main *maggie);
-
 #endif				/* __BPY_INTERNAL_IMPORT_H__ */