fix: removed hard-coded bitcoin Regnet chainID in E2E withdraw tests

[ws4charlie]

Description

Removed hard-coded bitcoin chainID in E2E withdraw tests.

Closes:

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Include instructions and any relevant details so others can reproduce.

• Tested CCTX in localnet
• Tested in development environment
• Go unit tests
• Go integration tests
• Tested via GitHub Actions

Checklist:

• I have added unit tests that prove my fix feature works

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.10%. Comparing base (6fab9e2) to head (9c4d303).

❗ Current head 9c4d303 differs from pull request most recent head 74cc686

Please upload reports for the commit 74cc686 to get more accurate results.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2240      +/-   ##
===========================================
+ Coverage    68.08%   68.10%   +0.01%     
===========================================
  Files          259      259              
  Lines        16032    16042      +10     
===========================================
+ Hits         10915    10925      +10     
  Misses        4658     4658              
  Partials       459      459              

Files	Coverage Δ
pkg/chains/bitcoin.go	100.00% <100.00%> (ø)