chore(test) remove Go module for xDS test client

[jpeach]

Summary

Remove Go module for xDS test client.

Full changelog

N/A

Issues resolved

This updates #2200.

Documentation

N/A

Testing

• Unit tests
• E2E tests
• Manual testing on Universal
• Manual testing on Kubernetes

[jpeach]

Looks like some Envoy v2 dependencies still here:

$ make run -C ./pkg/test/xds/client
make: Entering directory '/home/jpeach/upstream/konghq/kuma/pkg/test/xds/client'
go run main.go run --total "10" --xds-server-address "grpcs://localhost:5678"
2021-07-05T09:07:02.908+1000	INFO	kuma-xds-client.run	going to start xDS clients (Envoy simulators)	{"total": 10}
2021-07-05T09:07:02.908+1000	INFO	kuma-xds-client.run.envoy-simulator	creating an xDS client ...	{"idx": 0, "ID": "default.dataplane-0"}
2021-07-05T09:07:02.908+1000	INFO	kuma-xds-client.run.envoy-simulator	creating an xDS client ...	{"idx": 1, "ID": "default.dataplane-1"}
2021-07-05T09:07:02.908+1000	INFO	kuma-xds-client.run.envoy-simulator	creating an xDS client ...	{"idx": 2, "ID": "default.dataplane-2"}
2021-07-05T09:07:02.908+1000	INFO	kuma-xds-client.run.envoy-simulator	creating an xDS client ...	{"idx": 3, "ID": "default.dataplane-3"}
2021-07-05T09:07:02.908+1000	INFO	kuma-xds-client.run.envoy-simulator	creating an xDS client ...	{"idx": 4, "ID": "default.dataplane-4"}
2021-07-05T09:07:02.908+1000	INFO	kuma-xds-client.run.envoy-simulator	creating an xDS client ...	{"idx": 5, "ID": "default.dataplane-5"}
2021-07-05T09:07:02.908+1000	INFO	kuma-xds-client.run.envoy-simulator	creating an xDS client ...	{"idx": 6, "ID": "default.dataplane-6"}
2021-07-05T09:07:02.908+1000	INFO	kuma-xds-client.run.envoy-simulator	creating an xDS client ...	{"idx": 7, "ID": "default.dataplane-7"}
2021-07-05T09:07:02.909+1000	INFO	kuma-xds-client.run.envoy-simulator	creating an xDS client ...	{"idx": 8, "ID": "default.dataplane-8"}
2021-07-05T09:07:02.909+1000	INFO	kuma-xds-client.run.envoy-simulator	creating an xDS client ...	{"idx": 9, "ID": "default.dataplane-9"}
2021-07-05T09:07:04.880+1000	INFO	kuma-xds-client.run.envoy-simulator	opening an xDS stream ...	{"idx": 8, "ID": "default.dataplane-8"}
2021-07-05T09:07:04.888+1000	INFO	kuma-xds-client.run.envoy-simulator	requesting Listeners	{"idx": 8, "ID": "default.dataplane-8"}
2021-07-05T09:07:04.889+1000	INFO	kuma-xds-client.run.envoy-simulator	closing an xDS stream ...	{"idx": 8, "ID": "default.dataplane-8"}
2021-07-05T09:07:04.889+1000	INFO	kuma-xds-client.run.envoy-simulator	closing a connection ...	{"idx": 8, "ID": "default.dataplane-8"}
Error: one of xDS clients (Envoy simulators) terminated with an error: failed to request "type.googleapis.com/envoy.api.v2.Listener": EOF

[codecov-commenter]

Codecov Report

Merging #2280 (9508897) into master (cc0cb70) will increase coverage by 0.09%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #2280      +/-   ##
==========================================
+ Coverage   51.69%   51.79%   +0.09%     
==========================================
  Files         909      915       +6     
  Lines       41175    41392     +217     
==========================================
+ Hits        21284    21437     +153     
- Misses      17869    17904      +35     
- Partials     2022     2051      +29     

Impacted Files	Coverage Δ
pkg/test/xds/client/main.go	0.00% <0.00%> (ø)
pkg/xds/generator/direct_access_proxy_generator.go	80.26% <0.00%> (-1.32%)	⬇️
...k8s/native/controllers/proxytemplate_controller.go	0.00% <0.00%> (ø)
...kg/plugins/resources/k8s/native/pkg/test/within.go	100.00% <0.00%> (ø)
api/internal/util/proto/proto.go	62.50% <0.00%> (ø)
api/internal/util/proto/types.go	100.00% <0.00%> (ø)
pkg/test/xds/client/stream/client.go	0.00% <0.00%> (ø)
api/mesh/v1alpha1/dataplane_helpers.go	77.84% <0.00%> (+1.70%)	⬆️
api/mesh/v1alpha1/dataplane_insight_helpers.go	80.24% <0.00%> (+4.93%)	⬆️
... and 15 more

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[jakubdyszkiewicz]

Yeah, that should be V3. Merging this since the scope of this PR is to get rid of nested go module.