Fix commented out line in `fmpi_mpi_exit()`

src/fmpi_mpi.c

@@ -93,7 +93,7 @@ int fmpi_mpi_exit(struct fmpi_mpi_ctx ** const ctx)
     if(fmpi_mpi_check_error(*ctx, err_id, "MPI_Finalize") == true) {
         err_id = -1;
     }
-    //free(*ctx); *ctx = NULL;
+    free(*ctx); *ctx = NULL;
     return err_id;
 }
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