Fix outdated hardware wallet signing example

[vedant-asati]

Updates the "Signing with a hardware or external wallet" example in the tx package documentation to use the current API.
Fixes #3989

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.40%. Comparing base (ee42ec5) to head (316d6c0).

Additional details and impacted files

Flag	Coverage Δ
block	84.33% <ø> (ø)
blockchain	89.32% <ø> (ø)
client	67.58% <ø> (?)
common	97.45% <ø> (ø)
devp2p	86.78% <ø> (ø)
evm	73.11% <ø> (ø)
mpt	90.00% <ø> (+0.25%)	⬆️
statemanager	69.06% <ø> (ø)
static	99.11% <ø> (ø)
tx	89.89% <ø> (ø)
util	89.16% <ø> (ø)
vm	55.50% <ø> (ø)

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[acolytec3]

Thanks for the PR. Did you check this with the ledger signer app to verify this works?