Removed deprecated message factory

[tpazderka]

• Any changes relevant to users are recorded in the CHANGELOG.md.
• The documentation has been updated, if necessary.
• New code is annotated.
• Changes are covered by tests.

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[codecov-io]

Codecov Report

Merging #676 into master will increase coverage by 0.23%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #676      +/-   ##
==========================================
+ Coverage   63.69%   63.93%   +0.23%     
==========================================
  Files          64       64              
  Lines       11826    11642     -184     
  Branches     2091     2053      -38     
==========================================
- Hits         7533     7443      -90     
+ Misses       3697     3626      -71     
+ Partials      596      573      -23

Impacted Files	Coverage Δ
src/oic/extension/message.py	91.3% <ø> (+7.65%)	⬆️
src/oic/oauth2/message.py	74.06% <ø> (+0.34%)	⬆️
src/oic/oic/message.py	70.46% <100%> (+0.94%)	⬆️
src/oic/utils/settings.py	0% <0%> (-86.21%)	⬇️
src/oic/extension/client.py	38.57% <0%> (-0.47%)	⬇️
src/oic/utils/http_util.py	69.74% <0%> (-0.09%)	⬇️
src/oic/utils/rp/__init__.py	0% <0%> (ø)	⬆️
src/oic/oauth2/provider.py	71.16% <0%> (+0.37%)	⬆️
src/oic/oic/provider.py	74.6% <0%> (+0.41%)	⬆️
... and 5 more

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[tpazderka]

For some reason, the integration tests on this branch fail before they even start. This is not happening on any other PR although the travis config is the same in this respect...

I will have to investigate.

[tpazderka]

OK, the oidctest library relies on the removed factory, that is the reason for failures.

Will need to update the code and wait for merge.