Revert "CI: use walnascar branches"

This switches CI back to using the master branches.

Currently there are two known failures:
- sbsa-ref
- perf on musl

This reverts commit e0c1f0f94a3e3827f1e8bf0922b62617fd0c073f.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Jon Mason <jon.mason@arm.com>

ci/base.yml

@@ -7,7 +7,7 @@ distro: poky
 
 defaults:
   repos:
-    branch: walnascar
+    branch: master
 
 repos:
   meta-arm:

ci/meta-virtualization.yml

@@ -8,4 +8,3 @@ header:
 repos:
   meta-virtualization:
     url: https://git.yoctoproject.org/meta-virtualization
-    branch: master