Remove obsolete MSVC check from pragma guard

 git grep -h -B1 "^#\s*pragma once" | grep -v pragma | sort | uniq

is now clean.

[SVN r85952]

Author: steveire

include/boost/program_options.hpp

@@ -8,7 +8,7 @@
 #ifndef PROGRAM_OPTIONS_VP_2003_05_19
 #define PROGRAM_OPTIONS_VP_2003_05_19
 
-#if defined(_MSC_VER) && _MSC_VER >= 1020
+#if defined(_MSC_VER)
 #pragma once
 #endif