test: fix linting for the v5.x branch

PR-URL: #4547
Reviewed-By: Myles Borins <myles.borins@gmail.com>

Author: Fishrock123

test/sequential/test-pump-file2tcp.js

@@ -28,7 +28,6 @@ server.listen(common.PORT, function() {
 });
 
 var buffer = '';
-var count = 0;
 
 server.on('listening', function() {
 });