Remove extraneous top-level struct args to IsAnyNilOrZero

[aarongable]

We frequently call core.IsAnyNilOrZero(obj, obj.field), to check both that the object (usually a gRPC request) is not nil, and that the required field on the object is not nil. This is pointless for two reasons:

1. gRPC guarantees that the request object will never be nil, so checking the top-level object is wasted effort.
2. If the object were nil, then attempting to pass obj.field as the second argument to IsAnyNilOrZero will result in a nil pointer dereference panic before that function even gets to evaluate its first argument. This can be seen here: https://go.dev/play/p/duQK2ZbnxqK

Remove these extraneous first arguments, and operate under the assumption that the request object itself is never nil.