core: Clean up filename utility API

Remove more unused functions, and change pathname splitting to handle
more cases like duplicate //, and to throw an error on .. as a filename.

src/libotutil/ot-unix-utils.h

@@ -43,16 +43,9 @@ void ot_util_fatal_literal (const char *msg) G_GNUC_NORETURN;
 
 void ot_util_fatal_gerror (GError *error) G_GNUC_NORETURN;
 
-gboolean ot_util_filename_has_dotdot (const char *path);
+gboolean ot_util_filename_validate (const char *name, GError **error);
 
-gboolean ot_util_validate_file_name (const char *name,
-                                     GError    **error);
-
-GPtrArray *ot_util_sort_filenames_by_component_length (GPtrArray *files);
-
-GPtrArray* ot_util_path_split (const char *path);
-
-char *ot_util_path_join_n (const char *base, GPtrArray *components, int n);
+gboolean ot_util_path_split_validate (const char *path, GPtrArray **out_components, GError **error);
 
 void ot_util_set_error_from_errno (GError **error, gint saved_errno);