tools: remove obsolete npm test-legacy command

PR-URL: nodejs/node#5988
Reviewed-By: Myles Borins <[email protected]>

Makefile

@@ -169,7 +169,6 @@ test-npm: node
 	cd deps/npm ; npm_config_cache="$(shell pwd)/npm-cache" \
 	     npm_config_prefix="$(shell pwd)/npm-prefix" \
 	     npm_config_tmp="$(shell pwd)/npm-tmp" \
-	     PATH="../../:${PATH}" node cli.js run-script test-legacy && \
 	     PATH="../../:${PATH}" node cli.js run-script test && \
 	     PATH="../../:${PATH}" node cli.js prune --prod && \
 	     cd ../.. && \