Apply bandaid to symbols restarting in infinite loop

Created by: mrnugget

See my previous cries for help for context:

• https://sourcegraph.slack.com/archives/CHPC7UX16/p1585734381060100
• https://sourcegraph.slack.com/archives/C07KZF47K/p1585635858081000
• https://sourcegraph.slack.com/archives/C07KZF47K/p1583916442139400

Short version: symbols keeps restarting for me ever since I made that change in #8912

My current theory is that the existing check (which I'm changing here) doesn't work for symbols because:

1. In ./dev/go-install we use go install to build the symbols binary
2. Then we restart symbols
3. symbols "starts" by doing its own compilation, which changes a file in cmd/symbols/*
4. That causes handle-change.sh to restart the service that's currently compiling???

Yes, it's not complete...

Anyway: this here fixes it for me locally and since nobody else

1. complained about the same bug
2. asked for my changes in #8912

I'm hereby reverting the changes in #8912 for symbols.