If utf8 / utf16 is not your standard coding in Linux (which usually is not) then commands like “sed” will not work properly. On the other hand vi / vim editor is able to handle this coding without any problems. This editor has also ability to work from command line. So if you need to process more files you can try simple script like this:

for f in $(ls -1 *.csv); do echo $f; vi -c "%s/\"//g" -c "wq" $f; done

This simple example shows how to remove all double quotes from bunch of csv files. Results are stored in original file so make backup before you try it.