[libcxx] Make path::format a non-class enum

The spec doesn't declare it as an enum class, and being declared
as an enum class breaks referring to the values as e.g.
path::auto_format.

Differential Revision: https://reviews.llvm.org/D97084

GitOrigin-RevId: 26005c788b06755ccafe1205de181bbd8b2ed664
diff --git a/include/filesystem b/include/filesystem
index 2da24d4..58a1ef2 100644
--- a/include/filesystem
+++ b/include/filesystem
@@ -921,7 +921,7 @@
   typedef basic_string<value_type> string_type;
   typedef basic_string_view<value_type> __string_view;
 
-  enum class _LIBCPP_ENUM_VIS format : unsigned char {
+  enum _LIBCPP_ENUM_VIS format : unsigned char {
     auto_format,
     native_format,
     generic_format