Boot VM without bootloader - using init ramdisk

Remove ABL from the boot flow of VMs. Virtualization service uses
microdroid.json to construct the appropriate vm_config.

Partitions:
1. Boot related partitions (boot/init_boot/vendor_boot) are no more
   required. kernel & init ramdisk is directly passed via crosvm command
   line.
2. uboot_env is obsolete without ABL
3. bootconfig partition is no more required because we are attaching the
   bootconfigs to initrd image.

Bug: 240235424
Test: atest MicrodroidTestCase
Change-Id: I75c3ca83a40369013549ca83dcd208e80e6586bc
diff --git a/microdroid/microdroid.json b/microdroid/microdroid.json
index f02dcbf..00cedc8 100644
--- a/microdroid/microdroid.json
+++ b/microdroid/microdroid.json
@@ -1,21 +1,9 @@
 {
-  "bootloader": "/apex/com.android.virt/etc/fs/microdroid_bootloader",
+  "kernel": "/apex/com.android.virt/etc/fs/microdroid_kernel",
   "disks": [
     {
       "partitions": [
         {
-          "label": "boot_a",
-          "path": "/apex/com.android.virt/etc/fs/microdroid_boot.img"
-        },
-        {
-          "label": "init_boot_a",
-          "path": "/apex/com.android.virt/etc/fs/microdroid_init_boot.img"
-        },
-        {
-          "label": "vendor_boot_a",
-          "path": "/apex/com.android.virt/etc/fs/microdroid_vendor_boot.img"
-        },
-        {
           "label": "vbmeta_a",
           "path": "/apex/com.android.virt/etc/fs/microdroid_vbmeta.img"
         },
@@ -25,16 +13,6 @@
         }
       ],
       "writable": false
-    },
-    {
-      "partitions": [
-        {
-          "label": "uboot_env",
-          "path": "/apex/com.android.virt/etc/fs/uboot_env.img",
-          "writable": false
-        }
-      ],
-      "writable": true
     }
   ],
   "memory_mib": 256,