remove duplicate addZoneRange function

The cp argument wasn't being used, so just call the one that
doesn't take a cp argument.

src/MainWindow.cpp

@@ -820,7 +820,7 @@ MainWindow::setCriticalPower(int cp)
   // add a new range if we failed to find a valid one
   if (range < 0) {
     // create an infinite range
-    zones->addZoneRange(cp);
+    zones->addZoneRange();
     range = 0;
   }
 

src/Zones.cpp

@@ -744,12 +744,6 @@ void Zones::addZoneRange(QDate _start, QDate _end, int _cp)
     ranges.append(ZoneRange(_start, _end, _cp));
 }
 
-void Zones::addZoneRange(int _cp)
-{
-    (void) _cp; // TODO: _cp is unused.  Remove it?
-    ranges.append(ZoneRange(date_zero, date_infinity));
-}
-
 void Zones::addZoneRange()
 {
     ranges.append(ZoneRange(date_zero, date_infinity));
@@ -845,7 +839,7 @@ int Zones::insertRangeAtDate(QDate date, int cp) {
     int rnum;
 
     if (ranges.empty())
-	addZoneRange(cp);
+	addZoneRange();
     else {
 	rnum = whichRange(date);
 	assert(rnum >= 0);

src/Zones.h

@@ -60,7 +60,6 @@ class Zones : public QObject
         Zones() : defaults_from_user(false) {}
 
         void addZoneRange(QDate _start, QDate _end, int _cp);
-        void addZoneRange(int _cp);
         void addZoneRange();
 
         bool read(QFile &file);