Fix T103880: Crash with Line Art Grease-Pencil modifier

The line art modifier added a wmNotifier in it's
GpencilModifierTypeInfo.generateStrokes callback which isn't thread-safe
when called from the depsgraph. This was from the original inclusion
of the feature [0] however a more recent optimization to notifier
lookups [1] made the crash occur more frequently.

Remove the notifier as modifiers should not be adding WM level events
and it works without it.

[0]: 3e87d8a431
[1]: 0aaff9a07d

source/blender/gpencil_modifiers/intern/MOD_gpencillineart.c

@@ -44,9 +44,6 @@
 #include "MOD_gpencil_ui_common.h"
 #include "lineart/MOD_lineart.h"
 
-#include "WM_api.h"
-#include "WM_types.h"
-
 static void initData(GpencilModifierData *md)
 {
   LineartGpencilModifierData *gpmd = (LineartGpencilModifierData *)md;
@@ -168,8 +165,6 @@ static void generateStrokes(GpencilModifierData *md, Depsgraph *depsgraph, Objec
      * cache. */
     lmd->cache = gpd->runtime.lineart_cache;
   }
-
-  WM_main_add_notifier(NA_EDITED | NC_GPENCIL, NULL);
 }
 
 static void bakeModifier(Main *UNUSED(bmain),