Revert "Sculpt: Register sculpt brush op so it clears last operator panel"

This reverts commit 11bdc321a2.

This change caused T101743, in general OPTYPE_UNDO should not be used
to control the UI.

This also caused 2x undo pushes to be performed when sculpting,
although sculpt mode doesn't add a step for the second undo push
so it wasn't visible to the user.

An alternative fix will be applied separately as it's too risky this
close to a release.

source/blender/editors/sculpt_paint/sculpt.c

@@ -5863,7 +5863,7 @@ void SCULPT_OT_brush_stroke(wmOperatorType *ot)
   ot->ui = sculpt_redo_empty_ui;
 
   /* Flags (sculpt does own undo? (ton)). */
-  ot->flag = OPTYPE_BLOCKING | OPTYPE_REGISTER | OPTYPE_UNDO;
+  ot->flag = OPTYPE_BLOCKING;
 
   /* Properties. */