fix(internal/godocfx): retry go get with explicit envoy dependency

[tbpg]

This is a bit of a hack. Alternatively, we could capture stderr and check for the ambiguous import string before retrying.

This gets around errors of the form:

        github.com/envoyproxy/go-control-plane/envoy/type/matcher/v3: ambiguous import: found package github.com/envoyproxy/go-control-plane/envoy/type/matcher/v3 in multiple modules:

I confirmed this works by running it locally (fails before this commit, succeeds after):

go run . cloud.google.com/go/bigquery

I also removed the now-deprecated -d flag.