76b4acfa removed the shareMutex
parameter from RepositoryManager's constructor but did not remove the
corresponding documentation.

This fixes the following Clang warning:
.../kdevelop/kdevplatform/serialization/repositorymanager.h:26:15: warning: parameter 'shareMutex' not found in the function declaration [-Wdocumentation]
    ///@param shareMutex Option repository from where this repository should take the thread-safety mutex
              ^~~~~~~~~~