sapi: Remove dead code ext_transport_security.c using rijndael-alg-fst

This code depends on missing rijndael-alg-fst.h header,
so let's remove it this is not build.

It was used for S0 until S2 functions replaced them
( ver_0.0.6_RC1-97-gfcb244bb53  UIC-643: Use S2 encrypt functions in S0 )

After some investigations it looks like this code,
has been copied from ansestor project:

https://github.com/SiliconLabs/zipgateway/blame/zipgateway-7.18.03/src/serialapi/Serialapi.c#L3453

Since it looks buggy in many aspects
SupportsCommand(FUNC_ID_ZW_AES_ECB) is bypassed for some reasons.

Also rijndaelEncrypt is not returning an error on wrong arguments,
this is prone to misuse or malicious attacks.

After more investigations in zipgwateway
it looks like "rijndael-alg-fst.c"
was a copy of "Optimised C code v3.0" (under public domain).

I also note that upstream stated that:

IMPORTANT NOTE ! This code was written in order to clarify the mathematical description, and to run the statistical test.
Without modification, it should not be used to encrypt files, or for any other application.

And the downstream changes over that code are minimal.

So we can assyme the absent check were done on purpose,
since it is the fast version of the original "Reference code in ANSI C v2.2".

More cleanup may be needed to detect non built files.

Origin: #95
Relate-to: https://web.archive.org/web/20040831090650/http://www.esat.kuleuven.ac.be/~rijmen/rijndael/
Relate-to: https://web.archive.org/web/20040831090650/http://www.esat.kuleuven.ac.be/~rijmen/rijndael/rijndael-fst-3.0.zip
Relate-to: https://web.archive.org/web/20030403112845if_/http://www.esat.kuleuven.ac.be:80/~rijmen/rijndael/rijndaelref.zip
Bug-SiliconLabs: UIC-3660
Relate-to: SiliconLabsSoftware/z-wave-engine-application-layer#25
Signed-off-by: Philippe Coval <philippe.coval@silabs.com>

Author: rzr