Don't specify the C++ standard explicitely for Cppcheck
Don't specify the C++ standard explicitely for Cppcheck

Summary:
Cppcheck defaults the most recent standard by default, and this will
prevent from failing if the very latest `cppcheck` version is not used.

Test Plan:
  arc lint --everything

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D8517

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