All milk drinks produced by farmers or dairies and sold in milk bottles shall be exempt from the payment of soft drinks tax. The classification created by this section is made for the purpose of fostering and encouraging the dairy industry but should this classification be held discriminatory by either the courts of this State or of the United States and for that reason this section be held unconstitutional, then the classification created under this section shall not operate so as to render unconstitutional the remainder of this article but the exemption granted by this section shall thereupon cease.