I don't want to remove them completely because they can still be used
for inspiration for writing new tests, but to me, "skipped test"
implies "bug that needs to be fixed", and these aren't bugs so much as
outright outdated code.
Closes#6665
Not having prefer-const on the JS side makes JS -> TS refactors really
unreadable. This commit just auto-fixes it so we're using
`prefer-const` everywhere.