no more generated package doc

[jhump]

This would resolve #413. It relies on a flag that can be passed to protoc-gen-go.

[dsnet]

\cc @neild. We were discussing just removing this all together.

[neild]

The package doc comment is pretty useless at the moment. I can see a case for just removing it. I don't really have a strong opinion one way or the other, although I think I'd rather get rid of it always than add another knob.

[jhump]

@neild, how does it look now?

[paranoiacblack]

+1 to getting rid of this

[neild]

CL looks fine to me, I'll leave it up to @dsnet to decide whether we actually want to do this or not.

[dsnet]

I vote to remove it as well.

As it currently stands, it:

• provides no useful information. The list of .proto files is not particularly useful for the end user and the list of top-level messages is redundant with the godoc index.
  • One could argue that the index is overly-verbose because it contains other identifiers like: sub-messages (these sort nicely as they have the parent as a prefix), enums, grpc stubs, and oneof wrappers (it's unfortunate that we generate so many of these). If we did end up wanting to clean this up, perhaps use of per-file godoc sections is probably better to segregate the index so that all the oneof wrappers appeared at the end.
• actually conflicts with users who desire to put their own hand-written package documentation (which is almost always going to be more informative than what we can generate).