iwlwifi: remove 5.10 and 5.15 intermediate old firmwares

The iwlwifi firmware requirements between 5.10 and 5.15
for 20k series of chips jumped from v59 to v66 for
AXxxx series so we can drop the intermediate versions
as they're now unused.

Cc: Gregory Greenman <gregory.greenman@intel.com>
Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
Signed-off-by: Josh Boyer <jwboyer@kernel.org>