test: clear out onecase table

Signed-off-by: Manan Gupta <[email protected]>

go/vt/vtgate/planbuilder/testdata/onecase.json

@@ -1,7 +1,7 @@
 [
   {
     "comment": "Add your test case here for debugging and run go test -run=One.",
-    "query": "SELECT 1 WHERE (~ (1||0)) IS NULL",
+    "query": "",
     "plan": {
     }
   }