Merge #13457: tests: Drop variadic macro

Summary:
faf52f953b47aac6a39892b037eaa3f08d46b655 tests: Drop variadic macro (MarcoFalke)

Pull request description:

The C++11 constructor of `std::vector` that takes an initializer list, is not `explicit`. Thus, the macro is not required and can be dropped.

Hopefully fixes #13456

Tree-SHA512: 4095ed205f88138a7cd5b14790cc426899966f622a924a9b3f7de646a0d801a48ffb8921da760f1f93d5481298477c8a64dbec291381bb9aa77b075bdd2659f2

Backport of Core PR13457

Test Plan:

ninja check

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, jasonbcox

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D6671