chore: use blank identifier constants

[deelawn]

Replaces "_" with blank identifier constants.

[thehowl]

Looks good, except for the comment

[thehowl]

Did you forget to push the changes where you revert the changes in the comments?

[codecov]

Codecov Report

Attention: Patch coverage is 26.92308% with 19 lines in your changes are missing coverage. Please review.

Project coverage is 49.92%. Comparing base (3cc4952) to head (7e2bb75).
Report is 1 commits behind head on master.

Files	Patch %	Lines
gnovm/pkg/gnolang/preprocess.go	26.66%	4 Missing and 7 partials ⚠️
gnovm/pkg/gnolang/nodes.go	20.00%	1 Missing and 3 partials ⚠️
gnovm/pkg/gnolang/machine.go	0.00%	0 Missing and 2 partials ⚠️
gnovm/pkg/gnolang/helpers.go	0.00%	1 Missing ⚠️
gnovm/pkg/gnolang/values.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2158      +/-   ##
==========================================
- Coverage   49.93%   49.92%   -0.01%     
==========================================
  Files         576      576              
  Lines       77827    77827              
==========================================
- Hits        38864    38857       -7     
- Misses      35839    35845       +6     
- Partials     3124     3125       +1     

Flag	Coverage Δ
gnovm	44.94% <26.92%> (-0.03%)	⬇️

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