remove invalid example condition

[bshaffer]

I believe this is actually an incorrect condition. In protobuf, required arguments are allowed to move to optional without being considered a breaking change. So in this condition, the client libraries could potentially remove the overload, which would constitute a breaking change.

A more accurate example would be if all arguments in the signature are optional, which unfortunately I don't believe would ever happen with the method_signature annotation.

[alexander-fenster]

I believe there is a mix of terms here. The word "required" likely refers to the [(google.api.field_behavior) = REQUIRED] field annotation, not the field being required in the protobuf sense (which does not exist in proto3, which is the syntax we use). Removing the REQUIRED annotation is not considered a breaking change.

Upd. Fixed the very bad typo

[bshaffer]

I am also referring to the google.api.field_behavior sense. API fields can move from required to optional using that annotation. Therefore, something like that would break whatever method(s) were generated using method_signature

[noahdietz]

I agree with this point as, to both of your points, removing field_behavior = REQUIRED should not be a breaking change, which this example would create an opening for.

[noahdietz]

LGTM, but I'd like to let @alexander-fenster Approve the PR as he commented as well.