Remove uboot from the manifest

Since the uboot repository has been removed from android-kvm
syncing the manifest results in errors. Drop the line
which contains the uboot path from the manifest.

Change-Id: I8bc5af10cbce9fbeb52793de86a4d41d1ececc5d
Signed-off-by: Sebastian Ene <sebastianene@google.com>
diff --git a/default.xml b/default.xml
index 4b9fb9a..dcbaefe 100644
--- a/default.xml
+++ b/default.xml
@@ -12,7 +12,6 @@
   <project path="kvm-unit-tests" name="kvm-unit-tests" revision="kvmunittests" />
   <project path="linux" name="linux" revision="pkvm" />
   <project path="misc" name="misc" />
-  <project path="u-boot" name="u-boot" revision="pkvm" />
   <project path="trusted-firmware-a" name="trusted-firmware-a" revision="main" />
 
   <project path="prebuilts" name="prebuilts" clone-depth="1" />