runcommand: clear launch banner before starting

[cmitu]

The runcommand launch info screen will stay 'resident' under the emulator/port/etc. launched. While most of the time is not visible, it can show up when the launched program doesn't start full screen.

Note: this was reported in https://github.com/RetroPie/RetroPie-Setup/issues/3563 and with an attempted fix in https://github.com/RetroPie/RetroPie-Setup/pull/3564.