Walmart’s move -- depriving one of Wall Street’s elite firms of the talent atop its own foray into online banking -- underscores the seriousness of the retailer’s intent to intertwine itself in the financial lives of its customers. The audacious poaching punctuates years of warnings by bank leaders that their industry faces tough new challengers, after regulators smoothed the way for corporate giants and Silicon Valley to expand into payments and other services.