[8.18] [Obs AI Assistant] Update date category label (#213108) (#213136)

# Backport

This will backport the following commits from `main` to `8.18`:
- [[Obs AI Assistant] Update date category label
(#213108)](#213108)

<!--- Backport version: 9.6.6 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sorenlouv/backport)

<!--BACKPORT [{"author":{"name":"Viduni
Wickramarachchi","email":"viduni.wickramarachchi@elastic.co"},"sourceCommit":{"committedDate":"2025-03-04T16:20:12Z","message":"[Obs
AI Assistant] Update date category label
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AI Assistant] Update date category
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AI Assistant] Update date category label
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AI Assistant] Update date category label
(#213108)","sha":"ad8c3e7be5947931a25d6e07fabf13bef4230d89"}},{"branch":"8.x","label":"v8.19.0","branchLabelMappingKey":"^v8.19.0$","isSourceBranch":false,"state":"NOT_CREATED"}]}]
BACKPORT-->

Co-authored-by: Viduni Wickramarachchi <viduni.wickramarachchi@elastic.co>

x-pack/platform/packages/shared/kbn-ai-assistant/src/chat/conversation_list.tsx

@@ -142,9 +142,7 @@ export function ConversationList({
                   <EuiFlexItem grow={false} key={category}>
                     <EuiPanel hasBorder={false} hasShadow={false} paddingSize="s">
                       <EuiText className={titleClassName} size="s">
-                        {i18n.translate('xpack.aiAssistant.conversationList.dateGroup', {
-                          defaultMessage: DATE_CATEGORY_LABELS[category],
-                        })}
+                        {DATE_CATEGORY_LABELS[category]}
                       </EuiText>
                     </EuiPanel>
                     <EuiListGroup flush={false} gutterSize="none">