refactor: Remove redundant conditional
refactor: Remove redundant conditional

Summary:
This condition fMaster is already guaranteed to be true by the outer if.

Backport of Core [[https://github.com/bitcoin/bitcoin/pull/17971 | PR17971]]

Test Plan:
Trivial change. I just made sure I did not introduce any typo by checking that it compiles and tests still run succesfully.
`ninja && ninja check`

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7601

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