files: Rework the way fdinfos are collected

Now fdinfos are collected independently from reg files and
sockets. During tihs collect we effectively create the mirroring
list of both by checking which type-IDs are added first.

Fix this by removing the fdinfo_desc and attaching fds directly
to collected reg files and sockets. Pipes and unix sockets will
be reworked in the same manner soon.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/files.h

@@ -32,14 +32,6 @@ struct fmap_fd {
 	int			fd;
 };
 
-struct fdinfo_desc {
-	u32			id;
-	u32			type;
-	u64			addr;
-	int			pid;
-	struct list_head	list;
-};
-
 struct fdinfo_list_entry {
 	struct list_head	list;
 	int			fd;