Empty-op warning should not be printed when calling linearize

[baggepinnen]

julia> linearize(cs, inputs, outputs)
┌ Warning: An empty operating point was passed to `linearization_function`. An operating point containing the variables that will be changed in `linearize` should be provided. Disable this warning by passing `warn_empty_op = false`.

this warning only makes sense if the user calls the lower-level function themselves. When calling the higher-level linearize, there is no option to reuse the generated function and the warning is thus unnecessary.