[C++] Remove deprecated string-based Parquet encryption methods

[EnricoMi]

Describe the enhancement requested

In #46017 we have moved to storing encryption keys in SecureStrings. Existing string-based methods have been deprecated.

We want to encourage users to move to the new methods to improve encryption key security. For this, deprecated methods have to be removed so SecureString based methods are the sole way to pass encryption keys to Parquet.

Component(s)

C++