Revert "deps: Update dependency copy-webpack-plugin to v7"

[palango]

This reverts commit 4af4251.

Thank you for submitting this pull request :)

Fixes #2493
Related to #2481

Thore and I found out that the latest version of copy-webpack-plugin is also incompatible with webpack 4.x:

webpack-contrib/copy-webpack-plugin#575

Short description

Definition of Done

• Steps to manually test the change have been documented
• Acceptance criteria are met
• Change has been manually tested by the reviewer (dApp)

Steps to manually test the change (dApp)

[weilbith]

Thanks for the fix.
Here is the nightly test run that was successful with this fix.

[codecov]

Codecov Report

Merging #2495 (5c2a900) into master (9237372) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2495      +/-   ##
==========================================
+ Coverage   94.48%   94.49%   +0.01%     
==========================================
  Files         165      165              
  Lines        6670     6670              
  Branches     1092     1092              
==========================================
+ Hits         6302     6303       +1     
+ Misses        289      288       -1     
  Partials       79       79              

Flag	Coverage Δ
dapp	90.64% <ø> (ø)
dapp.unit	90.64% <ø> (ø)
sdk	96.23% <ø> (+0.02%)	⬆️
sdk.integration	69.69% <ø> (ø)
sdk.unit	85.57% <ø> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
raiden-ts/src/transfers/epics/withdraw.ts	93.57% <0.00%> (+0.91%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9237372...5c2a900. Read the comment docs.