[lib] introduce removeKeyserverActionType condition to keyserver reducer

Summary:
This diff adds the condition for removing a keyserver from the keyserver store. I am aware that at this time @inka currently has D9750 and D9820 up which refactor this reducer, and this diff might cause some merge conflicts. @inka and I have been communicating throughout this process and I will make @inka a blocking reviewer for this as well.

Linear task: https://linear.app/comm/issue/ENG-5465/introduce-remove-keyserver-action-case-to-reducekeyserver-function

Depends D9828

Test Plan:
Confirmed that I was able to remove a keyserver from the keyserver store

Reviewers: inka, rohan, michal

Reviewed By: inka

Subscribers: ashoat, tomek, wyilio, inka

Differential Revision: https://phab.comm.dev/D9829