Remove vendor/ (#688)

Vendoring seems to be problematic with go modules.
In addition to causing issues with transitive dependencies and being
problematic when trying to pull in the node-cli code, it also seems to
be pulling different versions than what is computed in go.mod.
This can be seen by comparing commits from the computed version in
go.mod with very small diffs (like a single Godep change in k8s) but massive
vendoring changes.

Basically I have very little confidence that this is even working.
This should be better in go1.13, but this is not released yet.

Makefile.e2e

@@ -36,7 +36,7 @@ e2e: NODE_NAME := vkubelet-mock-0
 e2e: export VK_BUILD_TAGS += mock_provider
 e2e: e2e.clean bin/e2e/virtual-kubelet skaffold/run
 	@echo Running tests...
-	cd $(PWD)/internal/test/e2e && go test -mod=vendor -v -timeout 5m -tags e2e ./... \
+	cd $(PWD)/internal/test/e2e && go test -v -timeout 5m -tags e2e ./... \
 		-kubeconfig=$(KUBECONFIG) \
 		-namespace=$(NAMESPACE) \
 		-node-name=$(NODE_NAME) \