scripted-diff: test: Remove brackets after assert

Summary:
Partial backport of core PR14954 (commit fa0e65b):
https://github.com/bitcoin/bitcoin/pull/14954/commits/fa0e65b77264476c61832542ab1a9dbedcc738ea#diff-a43dbc1d8db3be80406ee42e2142d7f0

Original scripted-diff:

-BEGIN VERIFY SCRIPT-
sed -i --regexp-extended -e 's/assert ?\((.+)\)(( )*)?(#.*)?$/assert
\1\3\3\4/g' $(git grep -l --extended-regexp 'assert ?\(' test)
-END VERIFY SCRIPT-

Test Plan:

./test/functional/test_runner.py --extended

Reviewers: #bitcoin_abc, deadalnix, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D4366