Igor Kushnir authored Feb 12, 2022 and Milian Wolff committed May 28, 2022

This function was called only from ItemRepositoryRegistry's destructor.
Move its implementation to ~ItemRepositoryRegistry() to make this clear.
Remove ItemRepositoryRegistryPrivate::m_mutex lock from
~ItemRepositoryRegistry() because a destructor of a class doesn't need
to lock its own mutex. Also remove the useless `m_path.clear();` line
from the destructor.

This commit does not affect KDevelop's behavior because
~ItemRepositoryRegistry() is never invoked. But the changes facilitate
understanding and even document that the code is dead.