Revert "Clean up external service updating UI code (#2033)"

Created by: tsenart

This reverts commit 62a0bb3e94a75fc6126c8e5dfaabbe92bbc2a9c5.

Reverting this commit fixes the weird behaviour I reported in https://github.com/sourcegraph/sourcegraph/issues/2227.

I don't know exactly why, because my TypeScript skills are lacking and I'd go down a rabbit hole to debug this.

Fixes #2227