cleanup patch

Here are two patches. First one just removes old code and adds some comments. It also adds a FLO check from gr-baz [1]

The second patch adds return value checks to i2c read/write operations. I haven't done it yet for the whole e4k driver, but will fix that if you think, this is a good idea. By now many i2c reads/writes aren't checked - I don't like that so I started catching it with assert. Thats not optimal but a least you notice when it fails. A device reset would be the best solution, but I'm not sure if we can do that form userspace.

[1] https://github.com/balint256/gr-baz/blob/master/lib/rtl2832-tuner_e4k.cc (l. 1036)