Do not override the optimizer's default parameters

[timokau]

Description

As discussed in #119. The
reasoning is that we don't have good reason to override those, the
library user will likely have to tune them anyways (or use a different
optimizer altogether). At the same time, they make the design proposed
in #119 (passing uninitialized optimizers and their parameters
separately) more difficult.

Motivation and Context

#119 (comment)

How Has This Been Tested?

Tests & pre-commit hooks.

Does this close/impact existing issues?

Part of #119 and thus part of #116.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.

[codecov]

Codecov Report

Merging #142 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #142   +/-   ##
=======================================
  Coverage   59.96%   59.96%           
=======================================
  Files         116      116           
  Lines        7658     7658           
=======================================
  Hits         4592     4592           
  Misses       3066     3066           

Impacted Files	Coverage Δ
csrank/choicefunction/cmpnet_choice.py	84.78% <ø> (ø)
csrank/choicefunction/fate_choice.py	91.30% <ø> (ø)
csrank/choicefunction/feta_choice.py	66.00% <ø> (ø)
csrank/choicefunction/ranknet_choice.py	81.63% <ø> (ø)
csrank/core/cmpnet_core.py	87.61% <ø> (ø)
csrank/core/fate_network.py	68.30% <ø> (ø)
csrank/core/feta_network.py	62.84% <ø> (ø)
csrank/core/ranknet_core.py	87.06% <ø> (ø)
csrank/discretechoice/cmpnet_discrete_choice.py	86.84% <ø> (ø)
csrank/discretechoice/fate_discrete_choice.py	94.44% <ø> (ø)
... and 7 more