Use ReadCondHandleKey::initialize(bool)

Use ReadCondHandleKey::initialize(bool) instead of

if (bool) {
  ReadCondHandleKey::initialize();
}

to automatically disable ReadCondHandleKey if it is not needed. https://acode-browser1.usatlas.bnl.gov/lxr/source/athena/Control/StoreGate/src/VarHandleKey.cxx#0110

This is a follow-up of !25960 (merged)