block: remove 'detached-header' option from opts after use

block: remove 'detached-header' option from opts after use

The code for creating LUKS devices references a 'detached-header'
option in the QemuOpts  data, but does not consume (remove) the
option.

Thus when the code later tries to convert the remaining unused
QemuOpts into a QCryptoBlockCreateOptions struct, an error is
reported by the QAPI code that 'detached-header' is not a valid
field.

This fixes a regression caused by

  commit e818c01ae6e7c54c7019baaf307be59d99ce80b9
  Author: Daniel P. Berrangé <berrange@redhat.com>
  Date:   Mon Feb 19 15:12:59 2024 +0000

    qapi: drop unused QCryptoBlockCreateOptionsLUKS.detached-header

which identified that the QAPI field was unused, but failed to
realize the QemuOpts -> QCryptoBlockCreateOptions conversion
was seeing the left-over 'detached-header' option which had not
been removed from QemuOpts.

This problem was identified by the 'luks-detached-header' I/O
test, but unfortunately I/O tests are not run regularly for the
LUKS format.

Fixes: e818c01ae6e7c54c7019baaf307be59d99ce80b9
Reported-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-ID: <20250919103810.1513109-1-berrange@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>