kuberay-tpu-webhook: remove webhook as pre-requisite target of docker-build (#305)

So contributors don't have to build the Go binary locally in order to build
the docker image.

Author: davidxia

applications/ray/kuberay-tpu-webhook/Makefile

@@ -25,7 +25,7 @@ deploy:
 	kubectl apply -f deployments/  
 
 # Build the docker image  
-docker-build: webhook  
+docker-build:
 	docker build . -t ${IMG} 
 
 # Push the docker image  
@@ -54,4 +54,4 @@ tests:
 	kubectl apply -f tests/
 
 delete-tests:
-	kubectl delete -f tests/
+	kubectl delete -f tests/