Remove boost from FunctionScore::addFunction because this is not support...

...ed by elasticsearch

So, I tested whether you can combine e.g. script_score with boost_factor, but that's not possible, if you add both to the function array it just takes the last one, in my case the boost_factor, and ignores the script_score function. So I removed the boost completely. 
Also, when thinking about it, I think it doesn't make any sense to have a boost there, if you want to boost the result you can just do so by e.g. defining your script in the script_score function so that it boosts how you want.