That command is wrong. You want

perl -CSD -Mutf8 -pe"s/’/'/g;"
[download]

-Cio has no effect in that example, which you can see by removing it.

$ echo It’s easy | perl -pe"s/’/'/g;"
It's easy
[download]

-Ci only has an effect if reading from a file

$ perl -Cio -pe"s/’/'/g;" <( echo "It’s easy" )
Wide character in print at -e line 1, <> line 1.
It’s easy
[download]

This is what you want if reading from a file:

$ perl -CiO -Mutf8 -pe"s/’/'/g;" <( echo "It’s easy" )
It's easy
[download]

This is what you want if reading from STDIN:

$ echo "It’s easy" | perl -CIO -Mutf8 -pe"s/’/'/g;"
It's easy
[download]

Combining both, you can use

perl -CiIO -Mutf8 -pe"s/’/'/g;"
[download]

Better:

perl -CSD -Mutf8 -pe"s/’/'/g;"
[download]