Cleanup: Remove scene frame macros (CFRA et al.)

Removes the following macros for scene/render frame values:
- `CFRA`
- `SUBFRA`
- `SFRA`
- `EFRA`

These macros don't add much, other than saving a few characters when typing.
It's not immediately clear what they refer to, they just hide what they
actually access. Just be explicit and clear about that.
Plus these macros gave read and write access to the variables, so eyesores like
this would be done (eyesore because it looks like assigning to a constant):
```
CFRA = some_frame_nbr;
```

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D15311

source/blender/draw/engines/eevee/eevee_engine.c

@@ -451,8 +451,8 @@ static void eevee_render_to_image(void *vedata,
   }
   EEVEE_PrivateData *g_data = ved->stl->g_data;
 
-  int initial_frame = CFRA;
-  float initial_subframe = SUBFRA;
+  int initial_frame = scene->r.cfra;
+  float initial_subframe = scene->r.subframe;
   float shuttertime = (do_motion_blur) ? scene->eevee.motion_blur_shutter : 0.0f;
   int time_steps_tot = (do_motion_blur) ? max_ii(1, scene->eevee.motion_blur_steps) : 1;
   g_data->render_timesteps = time_steps_tot;
@@ -588,7 +588,7 @@ static void eevee_render_to_image(void *vedata,
   /* Restore original viewport size. */
   DRW_render_viewport_size_set((int[2]){g_data->size_orig[0], g_data->size_orig[1]});
 
-  if (CFRA != initial_frame || SUBFRA != initial_subframe) {
+  if (scene->r.cfra != initial_frame || scene->r.subframe != initial_subframe) {
     /* Restore original frame number. This is because the render pipeline expects it. */
     RE_engine_frame_set(engine, initial_frame, initial_subframe);
   }