Use lastIndexOf to compute StringTools.startsWith in cpp

std/StringTools.hx

@@ -224,15 +224,6 @@ class StringTools {
 		return (cast s : java.NativeString).startsWith(start);
 		#elseif cs
 		return untyped s.StartsWith(start);
-		#elseif cpp
-		if (s.length < start.length)
-			return false;
-		var p0 = s.c_str();
-		var p1 = start.c_str();
-		for (i in 0...start.length)
-			if (p0.at(i) != p1.at(i))
-				return false;
-		return true;
 		#elseif hl
 		return @:privateAccess (s.length >= start.length && s.bytes.compare(0, start.bytes, 0, start.length << 1) == 0);
 		#elseif python