[docs] remove has_values and has_duals from documentation

[odow]

x-ref https://discourse.julialang.org/t/about-jump-is-solved-and-feasible/126868/3

People using has_values or has_duals are almost certainly using it wrong.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (3829fb2) to head (4c08fa8).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #3961   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           43        43           
  Lines         6085      6085           
=========================================
  Hits          6085      6085           

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