Remove button variant prop from Conditional Access page (#28290)

Support for this property was removed in
https://github.com/fleetdm/fleet/pull/28245, which merged just before
https://github.com/fleetdm/fleet/pull/27982. It's now causing linting
errors. I confirmed that the Save button looks the same without it.

<img width="793" alt="image"
src="https://github.com/user-attachments/assets/f3357cd2-1c4f-4c91-8c2e-e56797fb86e9"
/>

frontend/pages/admin/IntegrationsPage/cards/ConditionalAccess/ConditionalAccess.tsx

@@ -315,7 +315,6 @@ const ConditionalAccess = () => {
             />
             <Button
               type="submit"
-              variant="brand"
               disabled={!!size(formErrors)}
               className="button-wrap"
               isLoading={isUpdating}

frontend/pages/policies/ManagePoliciesPage/components/ConditionalAccessModal/ConditionalAccessModal.tsx

@@ -78,7 +78,6 @@ const ConditionalAccessModal = ({
             renderChildren={(disableChildren) => (
               <Button
                 type="submit"
-                variant="brand"
                 disabled={disableChildren || !isAdmin}
                 className="button-wrap"
                 isLoading={isUpdating}
@@ -104,9 +103,7 @@ const ConditionalAccessModal = ({
       <br />
       {learnMoreLink}
       <div className="modal-cta-wrap">
-        <Button onClick={onExit} variant="brand">
-          Done
-        </Button>
+        <Button onClick={onExit}>Done</Button>
       </div>
     </>
   );