BEIJING (Reuters) - China cannot delay tough economic reforms, Vice Premier Li Keqiang said on Sunday, underscoring the top leadership's push for market-based change after the sacking last week of an ambitious provincial leader who wanted a bigger state role in the economy. Li, widely expected to succeed Wen Jiabao as premier in a leadership transition that begins later this year, promised flexible policies to keep growth brisk and prices stable, with a focus on boosting domestic demand and pursuing structural reforms to make growth more stable and balanced. ...