Remove redundant check (!ecc is always true)

Summary:
Partial backport of Core PR10898 (commit 7466991)
https://github.com/bitcoin/bitcoin/pull/10898/commits/74669916709e5429990df120c6ba84ac60791b30

Test Plan: ninja check

Reviewers: deadalnix, Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2621