[libc++][NFC] Remove #endif comments for really small conditionals on _LIBCPP_HAS_NO_UNICODE_CHARS

We generally don't put a comment on the #endif when the #if block is so small
that it's unambiguous what the #endif refers to.

NOKEYCHECK=True
GitOrigin-RevId: 71752e00081cb4bc55d60c186cce1a18ed12e405
diff --git a/include/iosfwd b/include/iosfwd
index 499839f..974cb42 100644
--- a/include/iosfwd
+++ b/include/iosfwd
@@ -227,7 +227,7 @@
 #ifndef _LIBCPP_HAS_NO_UNICODE_CHARS
 typedef fpos<mbstate_t>    u16streampos;
 typedef fpos<mbstate_t>    u32streampos;
-#endif // _LIBCPP_HAS_NO_UNICODE_CHARS
+#endif
 
 #if defined(_NEWLIB_VERSION)
 // On newlib, off_t is 'long int'