op mode: T3355: remove the mention of legacy non-image installations

They were never supported by VyOS,
that was just for very old systens upgraded from Vyatta Core

(cherry picked from commit d8223d5)

python/vyos/version.py

@@ -81,16 +81,14 @@ def get_full_version_data(fname=version_file):
     else:
         version_data['system_type'] = f"{hypervisor} guest"
 
-    # Get boot type, it can be livecd, installed image, or, possible, a system installed
-    # via legacy "install system" mechanism
+    # Get boot type, it can be livecd or installed image
     # In installed images, the squashfs image file is named after its image version,
     # while on livecd it's just "filesystem.squashfs", that's how we tell a livecd boot
     # from an installed image
-    boot_via = "installed image"
-    if run(""" grep -e '^overlay.*/filesystem.squashfs' /proc/mounts >/dev/null""") == 0:
+    if run(""" grep -e '^overlay.*/filesystem.squashfs' /proc/mounts >/dev/null """) == 0:
         boot_via = "livecd"
-    elif run(""" grep '^overlay /' /proc/mounts >/dev/null """) != 0:
-        boot_via = "legacy non-image installation"
+    else:
+        boot_via = "installed image"
     version_data['boot_via'] = boot_via
 
     # Get hardware details from DMI