You do not need to change the line 24. Essentially all you did was change the variable name of the outFocalStatistics to inRaster2. The name in the geodatabase will always be "DEM_mean". However, it looks like you want to treat the "DEM_mean" as intermediate data. In that case just do not save the output of outFocalStatistics like this:
Execute FocalStatistics
outFocalStatistics = FocalStatistics(inRaster, neighborhood, "MEAN","")
Execute Minus
outMinus = inRaster - outFocalStatistics
Save the output
outMinus.save(outRaster)
This will always generate outFocalStatistics in memory and automatically delete it. On another note if you were to save the output of outFocalStatistics and want to delete it at the end of your script you would use arcpy.Delete_management(outFocalStatistics). The del function is useful when clearing variables, lists, dictionaries, and the like, but it will not delete output results.