Danvers cardiac device maker Abiomed Inc. won FDA approval to sell a new heart pump that is less invasive and delivers greater blood flow than a similar model it now markets. Abiomed said its Impella CP pump was approved under a clearance process that allows companies to skip clinical testing of devices that are ‘‘substantially equivalent’’ to those already on the market. In this case, Abiomed is rolling out a more powerful version of its ­­ I­mpella 2.5 pump.