ACPI: EC: Eliminate EC_FLAGS_QUERY_HANDSHAKE

The EC_FLAGS_QUERY_HANDSHAKE switch is never set in the current
code (the only function setting it is defined under #if 0) and
has no effect whatever, so eliminate it and drop the code
depending on it.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>