fix(docs): remove broken online codelabs page

[jakeva]

All 3 links on the web-labs page are broken or pointing to archived external content (two 404s, one archived Google Cloud doc). Since the page had no local content beyond these dead links, removing it entirely rather than updating w/ misleading refs.

Fixes spinnaker/spinnaker#7235 and #304

[jasonmcintosh]

ONLY concern... is something someplace is probably linking to this and ALSO would need to be removed...

[jakeva]

@jasonmcintosh Ah I forgot to mention, I did a quick search on the repo and found nothing linking to it:

$ grep -r "web-labs" --include="*.{md,html,yaml,yml,json,toml}" .
$

I did explore the idea of creating an "archived" page of some sort, but felt like it wasn't adding much value.