src: rename legacy.py into image.py

legacy.py contais mostly functions related to system images.
Rename the file to better represent the contents in it.

src/live/ogOperations.py

@@ -23,7 +23,7 @@ from src.ogRest import ThreadState
 from src.live.partcodes import GUID_MAP
 from src.live.parttypes import get_parttype
 
-from src.utils.legacy import *
+from src.utils.image import *
 from src.utils.net import ethtool
 from src.utils.menu import generate_menu
 from src.utils.fs import *