docs/user/*/install_upi: Drop compute replicas zeroing

We grew this in c22d042 (docs/user/aws/install_upi: Add 'sed' call
to zero compute replicas, 2019-05-02, openshift#1649) to set the stage for
changing the 'replicas: 0' semantics from "we'll make you some dummy
MachineSets" to "we won't make you MachineSets".  But that hasn't
happened yet, and since 64f96df (scheduler: Use schedulable masters
if no compute hosts defined, 2019-07-16, openshift#2004) 'replicas: 0' for
compute has also meant "add the 'worker' role to control-plane nodes".
That leads to racy problems when ingress comes through a load
balancer, because Kubernetes load balancers exclude control-plane
nodes from their target set [1,2] (although this may get relaxed
soonish [3]).  If the router pods get scheduled on the control plane
machines due to the 'worker' role, they are not reachable from the
load balancer and ingress routing breaks [4].  Seth says:

> pod nodeSelectors are not like taints/tolerations.  They only have
> effect at scheduling time.  They are not continually enforced.

which means that attempting to address this issue as a day-2 operation
would mean removing the 'worker' role from the control-plane nodes and
then manually evicting the router pods to force rescheduling.  So
until we get the changes from [3], it's easier to just drop this
section and keep the 'worker' role off the control-plane machines
entirely.

[1]: https://bugzilla.redhat.com/show_bug.cgi?id=1671136#c1
[2]: kubernetes/kubernetes#65618
[3]: https://bugzilla.redhat.com/show_bug.cgi?id=1744370#c6
[4]: https://bugzilla.redhat.com/show_bug.cgi?id=1755073

Author: wking

docs/user/aws/install_upi.md

@@ -18,19 +18,6 @@ $ openshift-install create install-config
 ? Pull Secret [? for help]
 ```
 
-### Empty Compute Pools
-
-We'll be providing the control-plane and compute machines ourselves, so edit the resulting `install-config.yaml` to set `replicas` to 0 for the `compute` pool:
-
-```sh
-python -c '
-import yaml;
-path = "install-config.yaml";
-data = yaml.load(open(path));
-data["compute"][0]["replicas"] = 0;
-open(path, "w").write(yaml.dump(data, default_flow_style=False))'
-```
-
 ## Edit Manifests
 
 Use [a staged install](../overview.md#multiple-invocations) to make some adjustments which are not exposed via the install configuration.

docs/user/gcp/install_upi.md

@@ -39,19 +39,6 @@ $ openshift-install create install-config
 ? Pull Secret [? for help]
 ```
 
-### Empty the compute pool (optional)
-
-If you do not want the cluster to provision compute machines, edit the resulting `install-config.yaml` to set `replicas` to 0 for the `compute` pool.
-
-```sh
-python -c '
-import yaml;
-path = "install-config.yaml";
-data = yaml.full_load(open(path));
-data["compute"][0]["replicas"] = 0;
-open(path, "w").write(yaml.dump(data, default_flow_style=False))'
-```
-
 ### Create manifests
 
 Create manifest to enable customizations which are not exposed via the install configuration.