Issue #1123 discusses a feature that allows users to set the cipher
security level. That feature wasn't built. It didn't provide enough
user value to justify the corresponding increase in complexity. The
feature request and the associated discussion threads were closed.
However, the proposed API spec and the TODO section remained in the
cipher docs. They're a vestige of that issue from olden days and this PR
removes those last living traces...
Fixes#8027.
