scripted-diff: Remove redundant sync_all and sync_blocks
Summary:
The sync calls are redundant after a call to generate, because generate already syncs itself.
Completes backport of core#23474:
https://github.com/bitcoin/bitcoin/pull/23474/commits/fa974f1f1417a536636347072e86bcb54a4c909c
Depends on D12533.
Test Plan:
ninja check-functional-extended
Reviewers: #bitcoin_abc, PiRK
Reviewed By: #bitcoin_abc, PiRK
Differential Revision: https://reviews.bitcoinabc.org/D12535