[build] makepchinput.py: fix names of cleaned files:

Before, makepchinput.py was not removing some files because they were misnamed (allLinkDef.h vs allLinkDefs.h, cppflags.txt vs allCppflags.txt).
Now, let the caller send consistent file names for "remove old files".
Remove duplicate allDict.cxx.h (sic!) removal.
Also remove allDict.cxx.pch which seems to exist, sometimes?