By Saeed Azhar and Niket Nishant NEW YORK (Reuters) – The biggest U.S. banks are expected to report weaker third-quarter profits as the economy slowed and volatile markets put the brakes on dealmaking. Four of the nation’s largest lenders – JPMorgan Chase & Co, Wells Fargo & Co, Citigroup Inc and Morgan Stanley – will report third-quarter earnings on Friday of next week. The results are expected to show a slide in net income after turbulent markets choked off investment-banking activity and lenders set aside more rainy-day funds to cover losses from borrowers who fall behind on their payments….