remove update time window

[gthao313]

We improve time window to use cron expressions, but currently we still support update time window. In future, we need deprecate update time window.

[stmcginnis]

I believe we are deprecating cron expressions in #351, right?

We actually need to track removal of the deprecated functionality after the deprecation period is over. We don't explicitly state a deprecation policy, so it might be good to clarify that somewhere so it's clear how long the functionality will remain deprecated before its removal.

[gthao313]

emm, Actually no. Currently brupop uses update time window. For being more flexible to schedule maintenance time window on users' purpose, we think Cron expression would be a better choice to enhance time window scheduler. So #351 is to implement new feature cron expression scheduler. However, we should consider the "backward compatibility", so we will still support update time window on next release, and then we will deprecate update time window this feature. Related issue: #343

so it might be good to clarify that somewhere so it's clear how long the functionality will remain deprecated before its removal.

This makes sense. I think we still support update time window settings for one more version 1.1.0, and we still deprecate it then.

[stmcginnis]

Deprecate means to communicate that the feature is no longer being actively supported and is planned to go away. That is the case with #351. Deprecate does not mean to remove. That is what happens after the deprecation period is over. It is no longer deprecated at that point - it is removed.

So right now, this is deprecated. Later on we plan to remove.