iwlwifi: remove 4.19 and 5.4 intermediate old firmwares

The iwlwifi firmware requirements between 4.19 and 5.4
for 20k series of chips jumped from v38 to v46 for 9xxx
and from v38 to v50 for AZxxx 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>