fix(Layer): `unmap` after `enter`

lua/libmodal/src/Layer.lua

@@ -183,10 +183,10 @@ function Layer:unmap(buffer, mode, lhs)
 
 		-- remove this keymap from the list of ones to restore
 		self.existing_keymaps_by_mode[mode][lhs] = nil
-	else
-		-- remove this keymap from the list of ones to create
-		self.layer_keymaps_by_mode[mode][lhs] = nil
 	end
+
+	-- remove this keymap from the list of ones managed by the layer
+	self.layer_keymaps_by_mode[mode][lhs] = nil
 end
 
 return Layer