[DOC] Remove outdated Resync Event section for Sync sources

Change in the documentation

Context:
Within the State Resync Events documentation, we describe how flagd handles synchronization when flags are deleted from one source. Historically, a resync was triggered in cases where a flag might also exist in another source, ensuring that the state from the secondary (less prioritized) source was taken into account. This was intended to mitigate potential user errors but introduced complexity and unpredictable behavior.

Problem:
With the changes introduced in #1797 , it was clarified that flagd does not currently handle cases where the same flagset ID is defined across multiple sources. This limitation is not reflected in the documentation, which still implies behavior that is not implemented. Specifically, flagd does not perform a resync or reconciliation between sources in such scenarios, leaving users to manage this complexity themselves. If unaddressed, this could lead to confusion or unexpected outcomes for users who rely on the outdated documentation.

Focus of this Ticket:

• Update the Documentation:
  Remove the outdated explanation of resync behavior in the State Resync Events section.
• Clarify Limitations:
  Explicitly document the current guideline: users must not specify flags with the same flagset ID in multiple sources. Highlight that flagd does not handle such scenarios and that users must configure their sources accordingly.
• Prevent Misunderstanding:
  Ensure the updated documentation communicates the potential risks or unexpected behavior that could occur if this guideline is not followed.

By addressing this, we will align the documentation with the actual behavior of flagd, ensuring clarity for users and reducing the likelihood of misconfiguration or confusion.

Open the linked State Resync Events section in the documentation and review the current explanation of resync behavior. Remove the outdated explanation, state that the same flagset ID must not be specified across multiple sources, and describe the risks of doing so. Done when the section matches the limitation described in this issue and no longer implies cross-source reconciliation.