jobs/swh-packages: Do not build binary wheel for swh-loader-svn package

The subversion loader now includes a C++ extension module so only generate
source distribution for PyPI upload as the binary wheel needs to be generated
on a dedicated docker image then repaired with the auditwheel tool.

So until our Jenkins pipeline supports building and repairing binary wheels
for linux platform, disable the binary wheel generation for swh-loader-svn.