ixgbevf: ixgbevf_q_vector clean up

ixgbevf: ixgbevf_q_vector clean up

Flex array should be at the end of the structure and use [] syntax

Remove unused fields of ixgbevf_q_vector.
They aren't used since busy poll was moved to core code in commit
508aac6dee02 ("ixgbevf: get rid of custom busy polling code").

Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Signed-off-by: Natalia Wochtman <natalia.wochtman@intel.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Rafal Romanowski <rafal.romanowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Link: https://patch.msgid.link/20251125223632.1857532-5-anthony.l.nguyen@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>