The following one liner will uninstall SSRS silently - replace [font="Courier New"]/qn[/font] with [font="Courier New"]/qb[/font] if you want to see the progress of the uninstall:

[font="Courier New"]setup.exe /qn REMOVE=RS_Server,RS_Web_Interface,RS_tools INSTANCENAME=myinstance[/font]

The default instance name is MSSQLSERVER