FRANKFURT (Reuters) - Euro zone growth could slow more than previously thought, the European Central Bank's Survey of Professional Forecasters indicated on Friday, underpinning the bank's signal to slow down the pace at which it removes stimulus.ECB President Mario Draghi warned on Thursday that a dip in the 19-member euro zone's growth could be deeper and longer than earlier forecast, comments widely seen as signalling a delay in the bank's first interest rate hike.The ECB's quarterly survey, a..