Merge #13913: qa: Remove redundant checkmempool/checkblockindex extra_args

Summary:
fa31ca0c22 qa: Remove redundant checkmempool/checkblockindex extra_args (MarcoFalke)

Pull request description:

They are already enabled by default for regtest:

https://github.com/bitcoin/bitcoin/blob/df9f71274645a917e2578c52a1c59745bce8112d/src/init.cpp#L1002-L1007

Closes  #13912. CC #12138

Tree-SHA512: b11a3e8cc4715569f917ab89132f8c8dcae64aebcd7a34182675f86cf7f6e207e3187b7ea01a56c92c8c3af76122b6b995e84f533e134676863f8953dc1f0574

Backport of Core PR13913

Test Plan:

test_runner.py

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, markblundeberg

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, markblundeberg

Differential Revision: https://reviews.bitcoinabc.org/D5104