[Task] Remove feature flag before 7.9 so that payment activity card becomes available to all merchants in 7.9.0

[jessy-p]

Part of #8680

In WooPayments 7.9, we will release the Payment Activity Card to all merchants. Therefore, this issue will remove the feature flag.

Ensure testing on WCCOM has completed before merging. See paJDYF-bWn-p2#comment-25037

[anu-rock]

This issue is about Reporting. Sending it to @Automattic/helix (ping @haszari ) as per our product responsibilities Pc2DNy-3z-p2, noting that Helix is already working on it.

[Jinksi]

As mentioned in the PR #9012, I've marked this as blocked – we must ensure testing on WCCOM has been completed before merging. See paJDYF-bWn-p2#comment-25037