Drop encoding= in Python 3.9

[pudo]

json.load() doesn't have encoding= in Python 3.9. Proposed fix.

[Rafiot]

Yep, looks good, I don't see a reason to keep the encoding set for any python version, as the file is already opened with the encoding set.

We will see if it causes problems with specific setups.

[coveralls]

Coverage decreased (-0.003%) to 36.944% when pulling 5016858 on pudo:python3.9 into ad483b6 on MISP:main.

[coveralls]

Coverage decreased (-0.003%) to 36.944% when pulling 5016858 on pudo:python3.9 into ad483b6 on MISP:main.