Remove last search term on backspace press when term finder is empty

Summary: Project doc: https://docs.google.com/document/d/1miofxds9DJgWScj0zFyBbdpRH5Rj0T9FqiCapof5-vU

Reviewed By: lblasa

Differential Revision: D48637890

fbshipit-source-id: fb952ffe1ab1a94d2bc465b89be6c62a71be9b9f

desktop/flipper-plugin/src/ui/PowerSearch/index.tsx

@@ -146,6 +146,14 @@ export const PowerSearch: React.FC<PowerSearchProps> = ({
             },
           ]);
         }}
+        onBackspacePressWhileEmpty={() => {
+          setSearchExpression((prevSearchExpression) => {
+            return prevSearchExpression.slice(
+              0,
+              prevSearchExpression.length - 1,
+            );
+          });
+        }}
       />
     </PowerSearchContainer>
   );