CI: track honister branch for clang and zephyr

These layers now have honister branches, so track those instead of master.

Signed-off-by: Ross Burton <ross.burton@arm.com>

ci/clang.yml

@@ -4,7 +4,6 @@ header:
 repos:
   meta-clang:
     url: https://github.com/kraj/meta-clang
-    refspec: master
 
 local_conf_header:
   clang: |

ci/meta-zephyr.yml

@@ -6,4 +6,3 @@ header:
 repos:
   meta-zephyr:
     url: https://git.yoctoproject.org/git/meta-zephyr
-    refspec: master