[mod] Drop Sphinx, since DuniterPy installs it in the CI

4 jobs for 1.2.0 in 9 minutes and 21 seconds (queued for 4 seconds)
Status Name Job ID Coverage
  Test
passed build_3_6 #60036
docker

00:03:14

passed build_3_7 #60037
docker

00:03:06

passed build_3_8 #60038
docker

00:03:15

passed build_3_9 #60039
docker

00:06:10