benchmark: remove excessive value from http2 benchmark

`requests = 1000000` took about 10 minutes per run for me
and doesn’t seem to add much value on its own.

PR-URL: #18936
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

benchmark/http2/respond-with-fd.js

@@ -7,7 +7,7 @@ const fs = require('fs');
 const file = path.join(path.resolve(__dirname, '../fixtures'), 'alice.html');
 
 const bench = common.createBenchmark(main, {
-  requests: [100, 1000, 10000, 100000, 1000000],
+  requests: [100, 1000, 10000, 100000],
   streams: [100, 200, 1000],
   clients: [1, 2],
   benchmarker: ['h2load']