remove unnecessary dependency (istio#276)

Author: nacx

Makefile.deps.mk

@@ -41,7 +41,7 @@ $(NPM_BIN):
 
 # Install Typescript generator if missing
 PROTOC_GEN_TS := ./node_modules/.bin/protoc-gen-ts
-$(PROTOC_GEN_TS): $(NPM_BIN)
+$(PROTOC_GEN_TS):
 	@echo "(re)downloading $@..."
 	@$(NPM_BIN) install