Remove rotation constraints

This should be an iOS SDK option, not hard coded into
low-level renderering.

Fixes #458

include/mbgl/map/map.hpp

@@ -115,7 +115,6 @@ public:
     void resetNorth();
     void startRotating();
     void stopRotating();
-    bool canRotate();
 
     // Debug
     void setDebug(bool value);

include/mbgl/map/transform.hpp

@@ -51,7 +51,6 @@ public:
     double getAngle() const;
     void startRotating();
     void stopRotating();
-    bool canRotate();
 
     // Transitions
     bool needsTransition() const;