[D1] disable -v2 message for typedef

After some experimenting with different transitional typedef implementation we have settled with mixin that injects same `typedef` for D1 version of the code and struct with same name and `alias this` for D2 version. This doesn't work very well with -v2 diagnostic as `typedef` statement still gets used and warned about.

As it is impossible to get a decent library implementation of typedef
in D1 (in absence of `alias this`) it is better to not warn about it and
rely on deprecation message of D2 compiler instead (which is essentially the same so nothing is lost here)