arch_init: Remove unnecessary default_config_files table

The existing default_config_files table in arch_init.c has a
single entry, making it completely unnecessary. The whole code
can be replaced by a single qemu_read_config_file() call in vl.c.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20170117180051.11958-1-ehabkost@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>