Use `ca.NewCA()` for generating certs and keys for the proxy injector
- Remove from CA controller everything that dealt with the
webhook/proxy-injector
- Remove no longer needed proxy-injector volumes for 'trust-anchors' and
'webhook-secrets'
- Remove from the proxy-injector the retrieval of the trust anchor and
secrets
- tls flag during install is no longer needed for auto-inject to work
Fixes#2095 and fixes#2166
Signed-off-by: Alejandro Pedraza <alejandro@buoyant.io>