[XRay] Remove scheduling dependency in fork_basic_logging.cc

Summary:
Continuation of https://reviews.llvm.org/D49501

Second part of the test has an scheduling order when there shouldn't be.



Reviewers: dberris, ormris

Reviewed By: dberris, ormris

Subscribers: TWeaver

Differential Revision: https://reviews.llvm.org/D49559

llvm-svn: 337724