MAINT: remove useless cell

docs/usage/dynamics.ipynb

@@ -423,31 +423,6 @@
     "The relativistic Breit-Wigner can be adapted slightly, so that its amplitude goes to zero at threshold ($m_0 = m1 + m2$) and that it becomes normalizable. This is done with {ref}`form factors <usage/dynamics:Form factor>` and can be obtained with the function {func}`.relativistic_breit_wigner_with_ff`:"
    ]
   },
-  {
-   "cell_type": "code",
-   "execution_count": null,
-   "metadata": {
-    "jupyter": {
-     "source_hidden": true
-    },
-    "tags": [
-     "hide-cell"
-    ]
-   },
-   "outputs": [],
-   "source": [
-    "from ampform.dynamics import (\n",
-    "    BreakupMomentumSquared,\n",
-    "    PhaseSpaceFactor,  # noqa: F401\n",
-    ")\n",
-    "from ampform.sympy.math import ComplexSqrt\n",
-    "\n",
-    "\n",
-    "def breakup_momentum(s: sp.Symbol, m1: sp.Symbol, m2: sp.Symbol) -> sp.Expr:\n",
-    "    q_squared = BreakupMomentumSquared(s, m1, m2)\n",
-    "    return ComplexSqrt(q_squared)"
-   ]
-  },
   {
    "cell_type": "code",
    "execution_count": null,