Remove visualization:useLegacyTimeAxis Advanced Setting

[markov00]

Back in 2021, the Data Vis team improved the elastic-chart time series chart by providing a multilayer time axis that gives a better time window context and improved label positioning over the existing time axis.

To test it in Kibana and receive feedback, we introduced the visualization:useLegacyTimeAxis flag.

Since then, the new time axis has been the default time axis used when rendering time series charts in Kibana. Only a small set of custom time charts, built by solution teams, are using the legacy time axis.

The goal is to finally set the multilayer time axis as the default implementation in Kibana.

Tasks:

• Removing the switch and relative code
• Refactor elastic-charts to remove the configuration/implementation and use the new implementation by default, this will automatically propagate the changes to every elastic-charts consumer (including the custom-built charts aka non-Lens charts).
• Refactor or mark the custom usage of time series charts in Kibana as changed to warn teams/consumers about that change.

[elasticmachine]

Pinging @elastic/kibana-visualizations (Team:Visualizations)