remove defaulting to query assist time range

Query assist enabled variable will gets reloaded based on http response
telling whether PPL agent is configured. The time range usually sets
before the response returns, which makes the time range to be last 40
years if query assist is enabled but not configured. Since time range
picker is removed from UI, this logic can also be removed.

(cherry picked from commit 0c03775)

Signed-off-by: Joshua Li <[email protected]>

public/components/event_analytics/explorer/log_explorer.tsx

@@ -18,13 +18,8 @@ import { EmptyTabParams, ILogExplorerProps } from '../../../../common/types/expl
 import { selectQueryResult } from '../redux/slices/query_result_slice';
 import { selectQueries } from '../redux/slices/query_slice';
 import { selectQueryTabs } from '../redux/slices/query_tab_slice';
-import { Explorer } from './explorer';
 import { getDateRange } from '../utils/utils';
-import {
-  QUERY_ASSIST_END_TIME,
-  QUERY_ASSIST_START_TIME,
-} from '../../../../common/constants/shared';
-import { coreRefs } from '../../../../public/framework/core_refs';
+import { Explorer } from './explorer';
 
 const searchBarConfigs = {
   [TAB_EVENT_ID]: {