CryptoSquare: add a test for "perfect square" normalized cipher text

[Trevoke]

The part of the readme that talks about how to normalize the cipher text is not very clear, an additional test would be helpful.

[robkeim]

A similar issue was discussed in more detail in #356.

[petertseng]

Alternatively, we could remove the tests entirely, as #750 suggests.

[petertseng]

Alternatively, we could remove the tests entirely

We did so in #922.