use the degree as parameter to the benchmarks

... instead of the number of bytes that does not really make any sense because we only consider one polynomial, i.e. only one column / shard of data.

the following relation between the degree of the polynomials and the size of the data holds still \text{deg}(P) = \frac{\#\text{bytes}}{k \times |f_r|} where |f_r| is the size of an element of the scalar finite prime field of the elliptic curve F_r and P is the polynomial of a single column / shard of data