spi_nor: remove unneeded enter_dpd() at end of spi_nor_configure()

This block of code was in the original commit that added
CONFIG_SPI_NOR_IDLE_IN_DPD but later modifications
added acquire_device() and release_device() calls
earlier in spi_nor_configure() and the release_device()
function will have already done the enter_dpd().

Signed-off-by: Mike J. Chen <mjchen@google.com>

drivers/flash/spi_nor.c

@@ -1414,11 +1414,6 @@ static int spi_nor_configure(const struct device *dev)
 	}
 #endif /* ANY_INST_HAS_MXICY_MX25R_POWER_MODE */
 
-	if (IS_ENABLED(CONFIG_SPI_NOR_IDLE_IN_DPD)
-	    && (enter_dpd(dev) != 0)) {
-		return -ENODEV;
-	}
-
 	return 0;
 }