String: Remove erase method, bindings can't mutate String

[akien-mga]

An alternative to removing this function would be to have it return a copy, like insert() does.

But there were only a handful of places using it and this was often not the most optimal approach anyway, so we might as well remove.

Part of #43311.

[akien-mga]

Proofread and tested briefly, seems to work as expected.

[DaGamingWolf]

for the record, i protest this. With erase() gone, now if we want to remove an invalid character from the smack dab middle of a text, it requires manually copying each character to an array just so that we can use the Array's erase() method, the text clean, then copy each character back from the array into the text. There's no way this is more optimal approach.

[vnen]

@DaGamingWolf you can see the implementation of String::erase() here and copy it to your script. It will be pretty much the same in terms of performance.