Remove link that has become problematic for linkcheck for some reason.

doc/notebooks/Box control for Formation Flying Satellites.ipynb

@@ -62,7 +62,7 @@
     "where $f_h$ is the perturbative acceleration acting on the satellite along the $\\hat{\\mathbf e}_h$ direction.\n",
     "\n",
     "## The Equations of Motion\n",
-    "We consider the dynamics of both the Chief and the Deputy expressed in terms of their position and velocity in $\\mathcal F_i$ and subject to the J2 term only (the expression of additional terms for the Earth gravitational potential can be found [here](https://space.stackexchange.com/questions/22266/j2-long-period-perturbations-in-the-inclination):\n",
+    "We consider the dynamics of both the Chief and the Deputy expressed in terms of their position and velocity in $\\mathcal F_i$ and subject to the J2 term only:\n",
     "\n",
     "$$\n",
     "\\left\\{\n",