When you review the settings for this activity, does it say the TV in on? If so, you either created you activity using the wrong activity type, or you told it to use the TV for the sound function. You can NOT remove device(s) that are providing the primary functions for a "standard" activity type. It will say "N/A" next to those device(s). The primary functions are determined by the activity type. For example, a "Watch TV" activity type requires 3 primary functions: Display, Tuner, and Sound. It will ask which device to use for each of the function. Some devices, like a TV, can provide more than one function. The "Listen to CD" activity type does not require a display but requires a sound device.

Note: If you need a custom activity that is not restricted by this rule, then select the "Utility" activity type.