Replace reference to "Google servers" in the docs

Several pages contain the following text (emphasis mine):

> With gRPC we can define our service once in a .proto file and implement clients
and servers in any of gRPC's supported languages, which in turn can be run in
environments ranging from **servers inside Google** to your own tablet - all the

Consider changing "servers inside Google" to something more partner neutral like:

> servers in a large data center

cc @lucperkins

Original context: https://github.com/grpc/grpc.io/pull/157#discussion_r395924613