By Devik Jain and David French (Reuters) – Wall Street’s main indexes dropped on Monday, giving up early gains in volatile trading, as investors adopted a cautious tinge ahead of the Federal Reserve meeting this week where policymakers are widely expected to raise interest rates. Complementing the weaker sentiment in equity markets, the yield on ten-year U.S. Treasuries hit 3% for the first time in more than three years, as traders positioned themselves for an expected half-point rate hike and the launch of “quantitative tightening,” where the central bank reduces its balance sheet after buyin…