migration: Delete redundant configuration

The qemu64 CPU model may cause incompatibility errors during
migration on some hosts. Removing this redundant setting ensures
broader compatibility.

Signed-off-by: lcheng <lcheng@redhat.com>

Author: cliping

libvirt/tests/cfg/migration/migrate_mem.cfg

@@ -33,7 +33,6 @@
             aarch64:
                 cpuxml_cpu_mode = "host-passthrough"
             cpuxml_fallback = "allow"
-            cpuxml_model = "qemu64"
             cpuxml_numa_cell = [{'id': '0', 'cpus': '0-1', 'memory': '1024', 'unit': 'MiB', 'discard': 'yes'}, {'id': '1', 'cpus': '2-3', 'memory': '1024', 'unit': 'MiB'}]
             setvm_max_mem_rt_slots = "16"
             setvm_max_mem_rt = 8192