Try to include the proper file :
#include "opencv2/videostab/videostab.hpp"
And change your code to :
CvPoint2D32f p0, p1;
vector<Point2f,allocator<Point2f>> ax, by;
ax.push_back(Point2f(2,2));
ax.push_back(Point2f(2,3));
ax.push_back(Point2f(2,4));
by.push_back(Point2f(3,2));
by.push_back(Point2f(3,3));
by.push_back(Point2f(3,4));
Mat t = videostab::estimateGlobalMotionLeastSquares(ax,by,3,0);