Reenable web-ssr after fixing Jetsam issues on iOS

In https://github.com/WebKit/JetStream/commit/d2a9536ef513df3a670b965bb807493bda80cc89 I had to disable the new web-ssr workload  since it was causing Safari to jetsam on iOS during the benchmark. I'm working on figuring out what went wrong and I'll make a PR to re-enable. CC @camillobruni 