Removed undocumented perftune.ini

[Stephan Bergmann]

FYI, 
<https://wiki.documentfoundation.org/index.php?title=ReleaseNotes/5.2&oldid=124119#General>: 
  "Support was removed for the undocumented perftune.ini flags 
FastPipeCommunication (core commit 
f8f87780f5f7be5ff185b0b8b3206d760d9dfed6) and 
QuickstartPreloadConfiguration (core commit 
d3084fb2442b9584b46fba743158c3fe46defa81)."

I assume nobody using LibreOffice was relying on those undocumented 
features that were added to OpenOffice.org/StarOffice back in the day.