Remove Previewnet

[jribbink]

Closes #1744

Description

Removes all remaining references to previewnet.

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For contributor use:

• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• Code follows the standards mentioned here
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 29.58%. Comparing base (9b92775) to head (614d78f).

Files with missing lines	Patch %	Lines
internal/prompt/prompt.go	0.00%	3 Missing ⚠️
internal/evm/gateway.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1750      +/-   ##
==========================================
+ Coverage   29.50%   29.58%   +0.07%     
==========================================
  Files          88       88              
  Lines        5161     5148      -13     
==========================================
  Hits         1523     1523              
+ Misses       3451     3438      -13     
  Partials      187      187              

Flag	Coverage Δ
unittests	29.58% <0.00%> (+0.07%)	⬆️

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