[lib] introduce removeKeyserverActionType

Summary:
This diff introduces the REMOVE_KEYSERVER redux action type as well as the RemoveKeyserverPayload type that we will need for this redux action. Since at this moment the disconnect keyserver functionality is not fully ready just yet, this action will just simply remove a keyserver (that's not actively connected) from keyserver store and the keyserver selection list.

Linear task: https://linear.app/comm/issue/ENG-5464/introduce-remove-keyserver-redux-action-type

Test Plan: flow

Reviewers: inka, rohan, michal

Reviewed By: rohan

Subscribers: ashoat, tomek, wyilio

Differential Revision: https://phab.comm.dev/D9806