Remove deprecated `PreparedStatementCache` and other long-deprecated API

[bschoening]

CachedPreparedStatementCreator, MapPreparedStatementCache, and PreparedStatementCache were deprecated on December 7, 2020 in DATACASS-833 and should be removed.

Class comments mention "Deprecated since 2.0. This class uses an unsafe, static held cache."

We agree these classes are unsafe and are seeing code which calls these functions sometimes fail on writes. Since these classes were deprecated in Dec 2020 it seems appropriate to entirely remove them now.

[mp911de]

I think it is now safe to remove these classes for the upcoming major revision as there have been deprecated for almost five years. We will also remove other deprecated API that has been deprecated during the 3.x development.

[bschoening]

@mp911de thanks for the reply. Given that these classes are marked as 'unsafe' and have, in our experience, led to failures in executing stored procedures, I would like to propose that this issue be considered a bug that could be addressed in version 4.x, vs waiting for version 5.x.

[mp911de]

The 4.x development line has reached with the version 4.5.x its planned last release, therefore the earliest version that can remove API is the 5.0 version.