fix(chart): improve sort_by_series description wording

Remove "secondary" from the description since sort_by_series and
sort_by_metric are independent controls — either can be used alone.
Clarify that the tiebreaker behavior only applies when both are enabled.

Fixes prettier formatting (+ at end of line, not beginning).

Author: Brian Donovan

superset-frontend/plugins/plugin-chart-word-cloud/src/plugin/controlPanel.tsx

@@ -43,9 +43,10 @@ const config: ControlPanelConfig = {
               label: t('Sort by series'),
               default: false,
               description: t(
-                'Include a secondary sort by series name (ascending). '
-                  + 'This produces consistent ordering when multiple series have the '
-                  + 'same metric value, but may reduce query performance on some databases.',
+                'Sort results by series name in ascending order. ' +
+                  'When combined with "Sort by metric", this acts as a tiebreaker ' +
+                  'for equal metric values. Adding this sort may reduce query ' +
+                  'performance on some databases.',
               ),
             },
           },