Remove python 2 support from ckbytelist constructor

[fuzzykat]

The problem: ckbytelist constructor checks python version for every byte in a loop:

for x in data:
    if sys.version_info[0] <= 2:
        # Python 2
        v = ord(x)
    else:
        # Python 3 and more
        v = x
    self.append(v)

which is redundant and not good for performance. I suppose, just checking python version once during module import would suffice. This PR removes support of python 2 from ckbytelist class, since python 2 is not supported anymore.

The performance issue can be illustrated with a simple benchmark command:

python3 -m timeit -s "import PyKCS11" "PyKCS11.ckbytelist(b'x'*100)"

For instance, on my system it now runs about six times faster compared to master.

[coveralls]

coverage: 87.164% (-0.05%) from 87.212%
when pulling 6f7c704 on fuzzykat:feature/ckbytelist
into f198974 on LudovicRousseau:master.

[LudovicRousseau]

I propose to just remove support of Python 2 for ckbytelist

Python 2 is no more supported since at least f4cb36e

[fuzzykat]

I propose to just remove support of Python 2 for ckbytelist

Python 2 is no more supported since at least f4cb36e

Done!

[LudovicRousseau]

Merged in bfb4e01

Thanks