The "SolarWinds Orion Toolset Integration Service" is running as process SWBrowserIntegration.exe and is by default installed into c:\Program Files\SolarWinds\Toolset.
Can you check it is not running?
Go into your services manager: Control Panel -> Administrative Tools -> Services
Look for the services named: SolarWinds Orion Toolset Integration Service
Stop this service.
Also, make sure that if your Tray area contains the "SolarWinds Toolset Integration" application you shut it down by right clicking its tray icon and selecting "Exit".
Retry the uninstall.
michalB replied while I was writing my response. To avoid any confusion "SWBrowserIntegration.exe" is the actual EXE name of the service which shows up in your service list as "SolarWinds Orion Toolset Integration Service".