Delete the conformance test (#808)

The conformance test is hard to run and heavily dependant on the exact
version of protoc installed on the developer's workstation.
Delete this from the v1 and leave conformance testing to v2,
which has infrastructure built for stricter control over dependencies.

Author: dsnet

Makefile

@@ -38,7 +38,6 @@ test:
 	go test ./... ./protoc-gen-go/testdata
 	go test -tags purego ./... ./protoc-gen-go/testdata
 	go build ./protoc-gen-go/testdata/grpc/grpc.pb.go
-	make -C conformance test
 
 clean:
 	go clean ./...