feat(crypto): CRP-2624 Move tECDSA/tSchnorr/vetKD fake canister to separate repo (#1042)

We decided to move the tECDSA/tSchnorr/vetKD mock/fake canister to a separate repository, as it is not really an example dapp, so this example dapp is deleted again. Originally, the code was added in #1029.

The new repository is https://github.com/dfinity/chainkey-testing-canister.

Author: fspreiss

.github/CODEOWNERS

@@ -69,7 +69,6 @@
 /rust/send_http_post/ @dfinity/growth
 /rust/simd/ @dfinity/execution
 /rust/threshold-ecdsa/ @dfinity/crypto-team
-/rust/threshold-mock/ @dfinity/crypto-team
 /rust/threshold-schnorr/ @dfinity/crypto-team
 /rust/token_transfer/ @dfinity/growth
 /rust/token_transfer_from/ @dfinity/growth