replace "dep" with "go mod"

A simple "go mod init && go mod tidy && go mod vendor" was enough and
mostly seems to have picked the same revisions of the dependencies as
before. Notable exceptions are klog and gogo/protobuf.

vendor/google.golang.org/grpc/Makefile

@@ -0,0 +1,60 @@
+all: vet test testrace
+
+build: deps
+	go build google.golang.org/grpc/...
+
+clean:
+	go clean -i google.golang.org/grpc/...
+
+deps:
+	go get -d -v google.golang.org/grpc/...
+
+proto:
+	@ if ! which protoc > /dev/null; then \
+		echo "error: protoc not installed" >&2; \
+		exit 1; \
+	fi
+	go generate google.golang.org/grpc/...
+
+test: testdeps
+	go test -cpu 1,4 -timeout 7m google.golang.org/grpc/...
+
+testappengine: testappenginedeps
+	goapp test -cpu 1,4 -timeout 7m google.golang.org/grpc/...
+
+testappenginedeps:
+	goapp get -d -v -t -tags 'appengine appenginevm' google.golang.org/grpc/...
+
+testdeps:
+	go get -d -v -t google.golang.org/grpc/...
+
+testrace: testdeps
+	go test -race -cpu 1,4 -timeout 7m google.golang.org/grpc/...
+
+updatedeps:
+	go get -d -v -u -f google.golang.org/grpc/...
+
+updatetestdeps:
+	go get -d -v -t -u -f google.golang.org/grpc/...
+
+vet: vetdeps
+	./vet.sh
+
+vetdeps:
+	./vet.sh -install
+
+.PHONY: \
+	all \
+	build \
+	clean \
+	deps \
+	proto \
+	test \
+	testappengine \
+	testappenginedeps \
+	testdeps \
+	testrace \
+	updatedeps \
+	updatetestdeps \
+	vet \
+	vetdeps