Fix compile warning in test code introduced by MB-16656 fix

We introduced a compile warning in ep_test_apis.cc as part of the fix for MB-16656:

redundant redeclaration of 'bool abort_msg(const char*, const char*, int)' in same scope [-Wredundant-decls]

This means that any following 4.1.x patches cannot have warnings checked to be zero as part of commit-validation.