Remove hasdynamicvalue function calls from rulenode2expr functions

[To5BG]

Remove hasdynamicvalue function calls from rulenode2expr functions because they cause issues with using _val as an evaluation cache for the Probe algorithm.

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 46.10%. Comparing base (aca61f9) to head (93bec01).

Files	Patch %	Lines
src/rulenode_operators.jl	66.66%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##              dev      #79   +/-   ##
=======================================
  Coverage   46.10%   46.10%           
=======================================
  Files           8        8           
  Lines         462      462           
=======================================
  Hits          213      213           
  Misses        249      249           

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[sebdumancic]

This looks fine to me, the original _val feature is not used anywhere. Shall we merge it without @Whebon's approval, as he is probably recovering after his defence? :)

[Whebon]

The original _val is not used anymore, making these checks are redundant. It seems like you have a new use-case for the _val field (otherwise the check returns false). Maybe we should add a docstring to RuleNode to clarify what _val is supposed to do and what format it is expected to be in.