Move fstab.microdroid to /system partition

Also this patch renames microdroid_vendor_ramdisk to
microdroid_fstab_ramdisk, since there is no vendor code there :)

Bug: 285855150
Test: build & install com.android.virt APEX
Test: adb shell /apex/com.android.virt/bin/vm run-microdroid
Test: atest MicrodroidTestApp
Change-Id: I3e4baba9ab6488216bfcaac90e81cf105ed2fb2e
diff --git a/microdroid/initrd/Android.bp b/microdroid/initrd/Android.bp
index 22a06e1..699a28a 100644
--- a/microdroid/initrd/Android.bp
+++ b/microdroid/initrd/Android.bp
@@ -32,7 +32,7 @@
     name: "microdroid_initrd_gen",
     srcs: [
         ":microdroid_ramdisk",
-        ":microdroid_vendor_ramdisk",
+        ":microdroid_fstab_ramdisk",
     ],
     out: ["microdroid_initrd.img"],
     cmd: "cat $(in) > $(out)",