Nikkei swoons as investors cut hedges against weaker yen

* Stocks, yen touch levels not seen since April 4 * Japan govt says need to watch stock market moves calmly * Japanese were net sellers of foreign bonds, stocks last week By Lisa Twaronite TOKYO, June 13 (Reuters) - The Nikkei stock average and the dollar skidded to lows on Thursday not seen since the day the Bank of Japan unveiled its massive monetary policy overhaul, as investors cut their long Japanese stocks and short yen positions. In a chicken-egg scenario, weakening J