Berkshire Hathaway, billionaire investor Warren Buffet's investment vehicle, unloaded its stake in GlaxoSmithKline during the fourth quarter of 2013, according to the US Securities and Exchange Commission (SEC).Previously, as of September 30th of 2013, Berkshire Hathaway held 1.511m shares in the British pharmaceutical giant, with a market value of $62.369m, regulatory filings published after the close of markets on February 14th revealed.AB