lscpu: remove the old code

lscpu: remove the old code

The file "/sys/firmware/dmi/tables/DMI" always exists.

The dmi_decode_cputype() can provide more information then arm_smbios_decode().
So remove it to tidy the code.

Before this patch, we can get the output from Centos 7.9 who has
"/sys/firmware/dmi/entries/4-0/raw" and "/sys/firmware/dmi/tables/DMI":
  ----------------------------------------------------
  BIOS Vendor ID:                  Ampere(TM)
  Model name：                     Neoverse-N1
    BIOS Model name:               Ampere(TM) Altra(TM) Processor
  ----------------------------------------------------

 After this patch which uses "/sys/firmware/dmi/tables/DMI", in Centos 7.9, we get:
  ----------------------------------------------------
  BIOS Vendor ID:                  Ampere(TM)
  Model name：                     Neoverse-N1
    BIOS Model name:               Ampere(TM) Altra(TM) Processor Q00-00 CPU @ 2.8GHz
    BIOS CPU family:               257
  ----------------------------------------------------

Signed-off-by: Huang Shijie <shijie@os.amperecomputing.com>