Add external/avb to the manifests.

Also remove external/bvb at the same time.
diff --git a/default.xml b/default.xml
index 4e8ac8c..b84057a 100644
--- a/default.xml
+++ b/default.xml
@@ -45,11 +45,11 @@
   <project path="device/generic/x86_64" name="device/generic/x86_64" groups="bdk" />
   <project path="external/aac" name="platform/external/aac" groups="bdk" />
   <project path="external/avahi" name="platform/external/avahi" groups="bdk" />
+  <project path="external/avb" name="platform/external/avb" groups="bdk" />
   <project path="external/autotest" name="platform/external/autotest" groups="bdk" />
   <project path="external/bison" name="platform/external/bison" groups="bdk" />
   <project path="external/boringssl" name="platform/external/boringssl" groups="bdk" />
   <project path="external/bsdiff" name="platform/external/bsdiff" groups="bdk" />
-  <project path="external/bvb" name="platform/external/bvb" groups="bdk" />
   <project path="external/bzip2" name="platform/external/bzip2" groups="bdk" />
   <project path="external/c-ares" name="platform/external/c-ares" groups="bdk" />
   <project path="external/chromite" name="platform/external/chromite" groups="bdk" />