[web] Cleanup plans-2026-phase-1 - phase 1: frontend (#34619)

* Remove `plans-2026-phase-1` from frontend in subscriptions module

* Remove `plans-2026-phase-1` from general frontend

* Remove empty `AiErrorAssistantPaywall`

* Simplify `UpgradeNotification`

* Update translations

* Fix tests

* Remove `OverleafAssistPaywall`

* Remove unused locales

GitOrigin-RevId: 4cf04bbde134a3f7b778a0695d388f31d9765343

services/web/frontend/js/features/ide-react/components/toolbar/upgrade-button.tsx

@@ -1,7 +1,6 @@
 import { useTranslation } from 'react-i18next'
 import * as eventTracking from '../../../../infrastructure/event-tracking'
 import OLButton from '@/shared/components/ol/ol-button'
-import { useFeatureFlag } from '@/shared/context/split-test-context'
 
 export default function UpgradeButton({
   className = '',
@@ -13,7 +12,6 @@ export default function UpgradeButton({
   source?: string
 }) {
   const { t } = useTranslation()
-  const plans2026 = useFeatureFlag('plans-2026-phase-1')
 
   function handleClick() {
     eventTracking.send('subscription-funnel', source, 'upgrade')
@@ -25,11 +23,7 @@ export default function UpgradeButton({
       <OLButton
         variant="premium"
         size="sm"
-        href={
-          plans2026
-            ? `/user/subscription/choose-your-plan?itm_referrer=${referrer}&paywall-type=${source}`
-            : `/user/subscription/plans?itm_referrer=${referrer}`
-        }
+        href={`/user/subscription/choose-your-plan?itm_referrer=${referrer}&paywall-type=${source}`}
         target="_blank"
         rel="noreferrer"
         onClick={handleClick}