Remove WITH_THR() and WITH_THX(), which are not used.

Remove WITH_THR() and WITH_THX(), which are not used.

grep.cpan.me and Google's codesearch find no use of WITH_THR or WITH_THX.

WITH_THX() was added in June 1999 in cea2e8a9dd23747f, and the last user
eliminated with 0b250b9ef0d5134f in August 1999. WITH_THX() was used again
for DEBUG_CX() in 1c98cc53150c4860, and eliminated in d9f81b50694a810f.

WITH_THR() was added in 1997 in 0f15f207c55ce70f. Use everywhere except
DEBUG_SCOPE() was eliminated in 2006 in 11206fddaf7ef068. WITH_THR() was
removed from DEBUG_SCOPE() in d9f81b50694a810f.