Remove unused variable
Remove unused variable

Summary: This is a partial backport of Core [[https://github.com/bitcoin/bitcoin/pull/15759 | PR15759]] : https://github.com/bitcoin/bitcoin/pull/15759/commits/26a93bce29fd813e1402b013f402869c25b656d1

Test Plan:
  ninja all check

Reviewers: #bitcoin_abc, nakihito

Reviewed By: nakihito

Differential Revision: https://reviews.bitcoinabc.org/D6399

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