Removed redundant explanation.

git-svn-id: http://svn.boost.org/svn/boost/trunk@83898 b8fc166d-592f-0410-95f2-cb63ce0dd405
Chrono: apply patch for #8435.

git-svn-id: http://svn.boost.org/svn/boost/trunk@83899 b8fc166d-592f-0410-95f2-cb63ce0dd405