How is this installed? I've not installed any graphics snapshots, so Im not sure if this haze texture is installed.

Go to the options page in ASA and then to the "Visibility Options" tab, inside this tab make sure there is a check mark next to "Disable Haze Layer". ASA then makes a backup of the haze texture currently installed in FSX and replaces it with a different one. To uninstall the texture remove the check mark from the box and ASA will swap the original backed up texture back again.