Remove grpc rpc

[felipejfc]

Remove GRPC RPC model as we will focus on NATS support only. It has proven rock stable and easier to manage in productive loads. It also enabled servers on different clouds/clusters to talk to each other given that all of them can talk to the NATS cluster for dispatching messages.

For the ones who liked GRPC more, both RPC server and Client in pitaya have interfaces and a method for you to replace the default one with your own implementation. So you can basically copy the grpc files to inside your project and use it.

[coveralls]

Pull Request Test Coverage Report for Build 10187728597

Details

• 7 of 35 (20.0%) changed or added relevant lines in 2 files are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.6%) to 58.588%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/docgenerator/descriptors.go	7	9	77.78%
pkg/client/protoclient.go	0	26	0.0%

Files with Coverage Reduction	New Missed Lines	%
pkg/app.go	3	66.15%

Totals
Change from base Build 10150830854:	-0.6%
Covered Lines:	4673
Relevant Lines:	7976

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💛 - Coveralls