Cleanup: various non-functional changes for C++ (python, windowmanager)

- Remove redundant void, struct.
- Use function style casts.

source/blender/python/intern/bpy_utils_previews.cc

@@ -178,7 +178,7 @@ static PyModuleDef bpy_utils_previews_module = {
     /*m_free*/ nullptr,
 };
 
-PyObject *BPY_utils_previews_module(void)
+PyObject *BPY_utils_previews_module()
 {
   PyObject *submodule;