Symbols tab always fetches the data onMount

Created by: dciug

Go to any file, e.g: https://sourcegraph.com/github.com/sourcegraph/sourcegraph@b887ad1/-/blob/cmd/frontend/internal/app/pkg/updatecheck/handler.go

Steps to reproduce:

1. Click on Symbols tab
2. Click on Files tab
3. Click on Symbols tab again

Expected behavior:

No loading, same as with the Files tab

Actual behavior:

Loading, fetches the Symbols again, every time you display that tab.