code: function( behavior ){
  
              var behaviors = this._behaviors;
  
              if (behavior){
  
                  for ( var i = 0, l = behaviors.length; i < l; ++i ){
  
                      if (behavior === behaviors[ i ]){
  
                          behaviors.splice( i, 1 );
                          behavior.setWorld( null );
  
                          this.emit( 'remove:behavior', {
                              behavior: behavior
                          });
  
                          break;
                      }
                  }
              }
  
              return this;
          }
docs: chainable
  Physics.world#removeBehavior( behavior ) -> this
  - behavior (Behavior): The behavior to remove
  
  Remove a behavior from the world