That 1" = 1' is referenced by all my Paper Space Page setups and probably most Annotative things as well. Save the drawing as a DXF. Open it in an ASCII text editor that can handle large files and substitute the new name for every occurance of 1" = 1'. Now open it AutoCAD and run AUDIT with Yes to fix errors and check your scale list again.
There are programmable ways to remove it, but the effect it would have on everything referencing it may destroy the drawing in the process.