Revert "make default_pro.prf advertize dynamically created .qmake.cache"

... and followup fixes.
this is not needed any more due to the breaking patch being reverted.

Change-Id: Ia3416fcc16ddece680efbd0322286a601879fa0a
Reviewed-by: Joerg Bornemann <joerg.bornemann@nokia.com>

mkspecs/features/default_pre.prf

@@ -47,9 +47,6 @@ CONFIG = lex yacc warn_on debug uic resources exceptions $$CONFIG
         error("Failed to run: $$MSG")
     }
 
-    # Let qmake know about the unexpectedly appearing cache file.
-    exists($$QMAKE_SYNCQT_OUTDIR/.qmake.cache):_QMAKE_CACHE_ = $$QMAKE_SYNCQT_OUTDIR/.qmake.cache
-
     unset(QTFWD)
     unset(PRO_BASENAME)
 }

qmake/project.cpp

@@ -1187,8 +1187,6 @@ QMakeProject::parse(const QString &t, QHash<QString, QStringList> &place, int nu
         }
         if(var == "REQUIRES") // special case to get communicated to backends!
             doProjectCheckReqs(vallist, place);
-        else if (var == "_QMAKE_CACHE_")
-            Option::mkfile::cachefile = varlist.isEmpty() ? QString() : varlist.at(0);
     }
     return true;
 }