linux-firmware/i915: Removing old Skylake DMC

This versions has the risk of  "DMC RAM corruption issue"
fixed on 1.23.

So let's remove old version and let only the latest one available
for now.

Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

WHENCE

@@ -2908,8 +2908,6 @@ Licence: Redistributable. See LICENCE.cavium for details
 
 Driver: i915 -- Intel Integrated Graphics driver
 
-File: i915/skl_dmc_ver1_21.bin
-File: i915/skl_dmc_ver1_22.bin
 File: i915/skl_dmc_ver1_23.bin
 
 File: i915/skl_dmc_ver1.bin