Update revision history

Author: pdimov

doc/smart_ptr/changelog.adoc

@@ -22,7 +22,6 @@ http://www.boost.org/LICENSE_1_0.txt
   been marked deprecated and will be removed in a future release.
 * Configurations that define `BOOST_NO_CXX11_HDR_ATOMIC` are no
   longer supported; a conforming {cpp}11 `<atomic>` is now required.
-* Consequently, Clang 3.5 and 3.6 are no longer supported.
 * The deprecated macros `BOOST_AC_USE_SPINLOCK`, `BOOST_AC_USE_PTHREADS`,
   `BOOST_SP_USE_SPINLOCK`, and `BOOST_SP_USE_PTHREADS` are no longer
   functional.