scripted-diff: rename GetSystemTimeInSeconds to GetTimeSeconds

Summary:
sed -i -e 's/GetSystemTimeInSeconds/GetTimeSeconds/g' $(git grep -l GetSystemTimeInSeconds src)

This is a backport of core#22107

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10958