[Deprecation] Redundant functionality core.relax_integrality and core.relax_discrete

[RomeoV]

Summary

There are currently two transformations both aimed at relaxing discrete variables here and here.
The core.relax_integrality transformation is very basic. It changes the domain to Reals for every variable, irregardless of the previous domain. It also set's the upper and lower bound.

core.relax_discrete is more sophisticated and tries to detect discrete variables and trnasform then to the continuous counterpart (i.e. NonNegativeIntegers->NonNegativeReals). The problem with the implementation is that is doesn't work for cloned models. See discussion in #995 and #326.

Additionally, there only exist tests for core.relax_integrality (as far as I can tell).

How to fix

Imo one of the two functionalities should be deprecated - probably the relax_integrality implementation. It should be noted that to use the functionality on clonded models (neccesary for many algorithms), currently relax_discrete does not work.

[blnicho]

Both of these transformations have been deprecated and replaced by the core.relax_integer_vars transformation.