We were selectively uploading it, but we were still gathering it,
which can be a waste of CPU.
Also remove a bunch of complexity that I don't think matters anymore.
And add an envknob to force service collection off on a single node,
even if the tailnet policy permits it.
Fixes#13463
Change-Id: Ib6abe9e29d92df4ffa955225289f045eeeb279cf
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>