The helper module bignum.py in the functional test framework contained many single-liner functions, which after refactoring only leave one function in the module. This single function is only used in script.py, so just move that function to script.py and remove the bignum.py module.provides only one function that is used outside the module (`bn2vch`) and it is used only in script.py, Remove `bignum.py` and move the function to `script.py`
PR17319 introduced a bug, so I had to merge also a commit from PR18378 which rewrites entirely the function `bn2vch`
This is a backport of Core [[https://github.com/bitcoin/bitcoin/pull/17319 | PR17319]]
Bugfix commit merged in the changeset:
https://github.com/bitcoin/bitcoin/pull/18378/commits/a3ad6459b77e9b7156e486a9e4a37dbfdc35e324
The rest of PR18378 will be in a separate diff.