I needed to downside a google not sans font file for android development.
I imported the file into glyphsapp and deleted the unwanted characters.
However, I keep getting a makeOTF error.
How can I remove unwanted glyphs without the makeOTF error?
You will need to remove all references to all the missing glyphs from your feature code.
If you just need a smaller font, you should look for subsetting tools. Opening a complex font like this is difficult to get properly exported again.