Remove old false positive avoidance code

From email explaining existence in the first place:

    This is from before when the used checks throwing false
    positives about unused due to changing the definition without
    checking whether it *had* a value to begin with and me not
    realizing they were false positives. I was thinking that it was
    warning from ARGC et. al. not being used since the previous
    macro or function call and the new value warning about
    overwriting the old value.

Source/cmFunctionCommand.cxx

@@ -112,7 +112,6 @@ bool cmFunctionHelperCommand::InvokeInitialPass
   // set the value of argc
   cmOStringStream strStream;
   strStream << expandedArgs.size();
-  this->Makefile->MarkVariableAsUsed("ARGC");
   this->Makefile->AddDefinition("ARGC",strStream.str().c_str());
   this->Makefile->MarkVariableAsUsed("ARGC");
 
@@ -121,7 +120,6 @@ bool cmFunctionHelperCommand::InvokeInitialPass
     {
     cmOStringStream tmpStream;
     tmpStream << "ARGV" << t;
-    this->Makefile->MarkVariableAsUsed(tmpStream.str().c_str());
     this->Makefile->AddDefinition(tmpStream.str().c_str(), 
                                   expandedArgs[t].c_str());
     this->Makefile->MarkVariableAsUsed(tmpStream.str().c_str());
@@ -156,10 +154,8 @@ bool cmFunctionHelperCommand::InvokeInitialPass
       }
     cnt ++;
     }
-  this->Makefile->MarkVariableAsUsed("ARGV");
   this->Makefile->AddDefinition("ARGV", argvDef.c_str());
   this->Makefile->MarkVariableAsUsed("ARGV");
-  this->Makefile->MarkVariableAsUsed("ARGN");
   this->Makefile->AddDefinition("ARGN", argnDef.c_str());
   this->Makefile->MarkVariableAsUsed("ARGN");