Revert "feat: AI entry button at the cell's bottom-right + clear input after success"

This reverts commit fd30e53e25.

src/components/opencode_inline_prompt.ts

@@ -367,12 +367,4 @@ export class OpenCodeInlinePrompt extends Widget {
     cell.model.sharedModel.setSource(text);
     Notification.info('已替换单元格内容');
   }
-
-  /**
-   * Clear the user input textarea (called by the cell action after a
-   * successful response, so the user can type a follow-up message).
-   */
-  clearInput(): void {
-    this._textarea.value = '';
-  }
 }