[Actions] Remove deprecated action configuration options

[YulNaumenko]

In the PR we deprecated the TLS related actions configuration options:
1.xpack.actions.rejectUnauthorized in favor of the new option xpack.actions.tls.verificationMode
2.xpack.actions.proxyRejectUnauthorizedCertificates in favor of the new option xpack.actions.tls.proxyVerificationMode.
3.xpack.actions.customHostSettings.tls.rejectUnauthorized in favor of the new option xpack.actions.customHostSettings.tls.verificationMode.

Deprecated options should be removed from the actions configuration, src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker and cloud.

This can be done when telemetry from #108716 shows usage is below 1% or deprecated for > 2.5 years.

[elasticmachine]

Pinging @elastic/kibana-alerting-services (Team:Alerting Services)

[pmuellr]

@mikecote Not sure if this is already included in 9.0 deprecation removal candidates or not ... if it is, I think we can close this, otherwise refer to it in a meta issue or whatever ...

[mikecote]

Thanks for the ping, I'll use this issue so when the time comes to remove the code, we can prioritize this work 👍 (keep open for now, prioritized soon)