refactor: simplify the internal shadow

Author: fang2hou

Modules/Combat/RaidMarkers.lua

@@ -211,9 +211,7 @@ function RM:CreateBar()
 	self:CreateButtons()
 	self:ToggleSettings()
 
-	if E.private.WT.skins.enable and E.private.WT.skins.windtools and E.private.WT.skins.shadow then
-		S:CreateBackdropShadow(self.bar)
-	end
+	S:CreateShadowModule(self.bar.backdrop)
 
 	E:CreateMover(
 		self.barAnchor,