empty directories in libstdc++-v3/testsuite on the trunk

[Matthias Klose]

There are three empty directories on the trunk. Ok to remove?

libstdc++-v3/testsuite/28_regex/13_ecmascript
libstdc++-v3/testsuite/28_regex/02_definitions
libstdc++-v3/testsuite/29_atomics/headers/stdatomic.h