accel: remove dead statement and useless assertion

accel: remove dead statement and useless assertion

ops is assigned again just below, and the result of the assignment must
be non-NULL.

Originally, the check for NULL was meant to be a check for the existence
of the ops class:

    ops = ACCEL_OPS_CLASS(object_class_by_name(ops_name));
    ...
    g_assert(ops != NULL);

(where the ops assignment begot the one that I am removing); but this is
meaningless now that oc is checked to be non-NULL before ops is assigned
(commit 5141e9a23fc, "accel: abort if we fail to load the accelerator
plugin", 2022-11-06).

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>