Remove include guard since it's no longer necessary

Author: smallp-o-p

libcxx/include/optional

@@ -201,6 +201,7 @@ namespace std {
 #  include <__config>
 #  include <__cstddef/ptrdiff_t.h>
 #  include <__exception/exception.h>
+#  include <__format/range_format.h>
 #  include <__functional/hash.h>
 #  include <__functional/invoke.h>
 #  include <__functional/unary_function.h>
@@ -250,10 +251,6 @@ namespace std {
 #  include <initializer_list>
 #  include <version>
 
-#  if _LIBCPP_STD_VER >= 26
-#    include <__format/range_format.h>
-#  endif
-
 // standard-mandated includes
 
 // [optional.syn]