TektonInstallerSet doesn't support Statefulset properly

[khrm]

Expected Behavior

When a statefulset in a TektonInstallerSet is removed, it should remove pod and statefulset that we configured in tektoninstallerset.

Actual Behavior

When a statefulset in a TektonInstallerSet is removed, it remains there.

Steps to Reproduce the Problem

1. Use any feature that utilizes statefulset like Add support for pipelines controller statefulset ordinals #2361 or Results without external DB in OpenShift.
2. Later on change from statefulset to deployment or internal to external DB, statefulset will remains.

[khrm]

/assign @khrm
According to discussion, we should delete installerset, it is expected behaviour.

[khrm]

I will raise a pr to fix this in Results.