System Information
Windows, GTX 1050ti

Blender Version
2.8, f074642b2cf

Short description of error
I'm not sure if this is intentional behavior, missing feature or a bug, but still reporting this, as it might be useful.
It seems like there's no option to bypass color management when saving non-exr files from compositor. Documentation states:

By default only renders are displayed and saved with the render view transformations applied. These are the Render Result and Viewer image data-blocks, and the files saved directly to a drive with the Render Animation operator.

In contrary to image "Save as" with "Save as render" option disabled File Output node assumes, that only linear data is "not a render". There's no way to export from compositor non-linear files like jpg or png that contain "non-color data" like normal maps, image masks, material masks, baked textures or intermediate beauty files with color management disabled. Saving files one by one for stills seems not to be workaround for animations...

Exact steps for others to reproduce the error
Just see File Output node options, there's no "Save as render"