Replace surface torque calculation

[jorgensd]

Instead of using:

TEAM30/utils.py

Lines 174 to 180 in d9ed381

	x = ufl.SpatialCoordinate(self.mesh)
	r = ufl.sqrt(x[0]**2 + x[1]**2)
	dF = 1 / mu_0 * ufl.dot(self.B, x / r) * self.B
	dF -= 1 / mu_0 * 0.5 * ufl.dot(self.B, self.B) * x / r
	torque = self.L * self._restriction * _cross_2D(x, dF)
	torque_surface = (torque("+") + torque("-")) * dS_air
	self._surface_torque = fem.form(torque_surface, form_compiler_options=self.fp, jit_options=self.jp)

we should use FEniCS/dolfinx@c348948