Revert "Add MSVC pragma for UTF-8 source code"

This reverts commit 89cbd4d953.

See discussion:
https://bugzilla.gnome.org/show_bug.cgi?id=747772

src/hb-private.hh

@@ -132,7 +132,6 @@ static int errno = 0; /* Use something better? */
 #  endif
 #  if defined(_MSC_VER) && _MSC_VER < 1900
 #    define snprintf _snprintf
-#    pragma execution_character_set("utf-8")
 #  endif
 #endif