Fix dependency on boost in playground app.

app/playground/main.cpp

@@ -10,7 +10,5 @@
 #include <pls/pls.h>
 
 int main() {
-  auto range = boost::irange(0, 10);
-  bool test = std::is_integral<typename std::remove_reference<decltype(range.begin())>::type>::value;
-  std::cout << test << std::endl;
+
 }