Replace strings.Index usages with strings.Cut

[WilczynskiT]

fixed #4928

[CLAassistant]

All committers have signed the CLA.

[mholt]

Thank you for opening a PR!

I think the purpose of using strings.Cut() is to split a string into two pieces. strings.Index() is still the right function to see if a substring can be found.

There are some uses of Index() that still seem simpler than using Cut(), IMO.

I think we'd only want to keep the changes in listeners.go, load.go, and addresses.go. The others seem to be more complicated or not quite the right fit.

There may also be some occurrences of SplitN() that we could replace with Cut(), if we are splitting only into 2 pieces.

[WilczynskiT]

@mholt Okey, thank you for review ;) I changed it. I will look at the SplitN() and will create new ticket to do it

[francislavoie]

I will look at the SplitN() and will create new ticket to do it

Please just do it in this PR, it'll be easier to review all in one place.

Also, please remember to sign the CLA.

To clarify, the intent of the issue I opened is to find places where we can use the new strings.Cut to simplify existing code. If some places have legitimate uses of the existing strings.* functions that are already simple, then there's no need to change that code.

[WilczynskiT]

Okey, I added the changes and signed the CLA. So it is ready to continue the review.

[mholt]

This LGTM!

Thank you for the contribution @WilczynskiT 😃