crypto: aead - Remove unused inline functions from aead

The aead_enqueue_request, aead_dequeue_request and aead_get_backlog
are no longer used since commit 04a4616e ("crypto: omap-aes-gcm
- convert to use crypto engine"), their functinoality has been
replaced by crypto engine, so remove them.

Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>