Removed last use of std::mutex from the rdbms library

With respect to the rdbms::SqliteStmt class. Replaced
std::mutex and std::lock_guard with their helgrind friendly
drop in replacements threading::Mutex and
threading::MutexLocker.

With respect to the rdbms::SqliteConn class. Replaced
std::mutex and std::lock_guard with their helgrind friendly
drop in replacements threading::Mutex and
threading::MutexLocker.

With respect to the rdbms::OcciStmt class. Replaced
std::mutex and std::lock_guard with their helgrind friendly
drop in replacements threading::Mutex and
threading::MutexLocker.

With respect to the rdbms::OcciRset class.  Replaced
std::mutex and std::lock_guard with their helgrind friendly
drop in replacements threading::Mutex and
threading::MutexLocker.

With respect to the rdbms::OcciEnvSingleton class. Replaced
std::mutex and std::lock_guard with their helgrind friendly
drop in replacements threading::Mutex and
threading::MutexLocker.

With respect to the rdbms::OcciConn class. Replaced std::mutex and
std::lock_guard with their helgrind friendly drop in replacements
threading::Mutex and threading::MutexLocker.

cta/CTA#87 cta-catalogue-delete-all-data and cta-catalogue-schema-drop should require interactive confirmation

Removed the now redundant locking commands for the catalogue schema.
These commands were made redundant when the cta-catalogue-schema-drop
command was made interactive.

Done.