Remove microdroid U-Boot environment

U-Boot now bakes an environment compatible with microdroid, and all the
workarounds in these files are obsolete. Keep an architecture-neutral
version of the environment around for future debugging use cases.

Bug: 180481192
Change-Id: I58d82010629f1d621577a1c2fdd3eb407f50211f
diff --git a/microdroid/uboot-env.txt b/microdroid/uboot-env.txt
index 0385b50..e5f8b79 100644
--- a/microdroid/uboot-env.txt
+++ b/microdroid/uboot-env.txt
@@ -1,12 +1 @@
-# Static u-boot environment variables for microdroid. See b/180481192
-
-# Boot the device following the Android boot procedure
-# `0` is the disk number of os_composite.img
-# `a` and `_a` are the slot index for A/B
-bootcmd=verified_boot_android virtio 0 a
-
-bootdelay=0
-fdtaddr=0x80000000
-
-# Microdroid doesn't use keymint yet
-android_keymint_needed=N
+# Empty environment for bootloader debugging