iwlwifi: remove old intermediate 5.15+ firmwares

iwlwifi: remove old intermediate 5.15+ firmwares

The iwlwifi firmware requirements since 5.15 for
for 20k series of chips was bumped from v66 to v72 for
AXxxx series in the 5.18 kernel so we can drop the
intermediate versions as they're now unused, it's
still the current highest rev firmware as of 6.2 cycle.

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