crypto: testmgr - remove workaround for AEADs that modify aead_request

Now that all AEAD algorithms (that I have the hardware to test, at
least) have been fixed to not modify the user-provided aead_request,
remove the workaround from testmgr that reset aead_request::tfm after
each AEAD encryption/decryption.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>