Switch to generated handshake tests

Replace `tests/opt-testcases/handshake-manual.sh` by
`tests/opt-testcases/handshake-generated.sh`. They are identical except for
comments, and for some extra dependencies on
`MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED` which are needed in `development,
but not in `mbedtls-3.6. Those dependencies don't hurt the useful coverage
of the tests, so we'll live with them.

Signed-off-by: Gilles Peskine <[email protected]>

Author: gilles-peskine-arm