refactor(ui): remove some superfluous ui_flush() calls

- <expr> mapping has no business saving and restoring the
  low-level UI cursor. The cursor will be put in a reasonable
  position after input is processed, chill out.
- TUI handles output needed for suspend
- vgetc() family of function does flushing

src/nvim/ex_docmd.c

@@ -4838,13 +4838,9 @@ static void ex_stop(exarg_T *eap)
   }
   apply_autocmds(EVENT_VIMSUSPEND, NULL, NULL, false, NULL);
 
-  // TODO(bfredl): the TUI should do this on suspend
-  ui_cursor_goto(Rows - 1, 0);
-  ui_call_grid_scroll(1, 0, Rows, 0, Columns, 1, 0);
+  ui_call_suspend();
   ui_flush();
-  ui_call_suspend();  // call machine specific function
 
-  ui_flush();
   maketitle();
   resettitle();  // force updating the title
   ui_refresh();  // may have resized window