coreos-x86_64-builder.bu: Remove Butane merge to align with aarch64 config

- Sync the x86_64 Butane config with the existing aarch64 configuration.
- This change eliminates the need for a special tofu-related modification,
as tofu already handles the merge automatically.

Signed-off-by: Renata Ravanelli <rravanel@redhat.com>

Author: ravanelli

multi-arch-builders/coreos-x86_64-builder.bu

@@ -6,10 +6,6 @@
 #
 variant: fcos
 version: 1.4.0
-ignition:
-  config:
-    merge:
-      - local: builder-common.ign
 passwd:
   users:
     - name: builder