Removal of `/remind_me` quick action

Summary

The /remind_me quick action was introduced as an experiment in %17.0. A lot has changed since then and this action is no-longer required. We have some code and some feature flags hanging around that need cleaning up. We may want to re-introduce it in another form, but until then we should keep the codebase clean(er).

Proposal

• Disable the remind_me_quick_action feature flag
• Remove all code related to the quick action
• Remove all tests related to the quick action
• Remove the remind_me_quick_action feature flag and all references to it.