Remove test_atomic.h header

Because <atomic> can now be used in C++03 there is no need for the test_atomic.h header.
This commit removes the header and converts all usages to use <atomic> instead.


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@245468 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed