drd/tests/std_thread: Remove two superfluous macro definitions

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14003 a5019735-40e9-0310-863c-91ae7b9d1cf9
drd manual: Fix C++11 instructions

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14004 a5019735-40e9-0310-863c-91ae7b9d1cf9