Re #8483. Remove unnecessary include.

Not strictly related to this ticket, but I was surprised when I made a
change in ImplicitFunctionParameter.h and everything recompiled.
This turned out the be the reason.
Re #8483. Don't leak memory via Poco XML calls.
Re #8483. Don't leak memory in Poco XML calls.
Re #8483. Don't leak memory in Poco XML calls.
Merge branch 'bugfix/8483_api_xml_memory_leaks' into develop