[Arista] Rely on automatic flash size detection for Lodoga (#8608)

Lodoga actually has a 8GB storage device.
LodogaSsd variant has a 30GB SSD drive.
However, in boot0 both were mishandled and assigned 4GB for legacy reasons.

Remove the hardcoding of the flash size and let boot0 autodetect the available space.

files/Aboot/boot0.j2

@@ -509,7 +509,6 @@ write_platform_specific_cmdline() {
     fi
     if [ "$sid" = "Lodoga" ]; then
         aboot_machine=arista_7050cx3_32s
-        flash_size=3700
     fi
     if [ "$sid" = "Marysville" ]; then
         aboot_machine=arista_7050sx3_48yc8