remove duplicate text in generic source docs

docs/source/user_guide/user_guide_reference_sources_generic_source.rst

@@ -134,20 +134,6 @@ Particle initial direction
       source.direction.phi = [0, 90 * deg]
 
 
-``direction.type = "iso"`` assigns directions to primary particles
-based on 𝜃 and 𝜙 angles in a `spherical coordinate system
-<https://en.wikipedia.org/wiki/Spherical_coordinate_system>`__.
-By default, 𝜃 varies from 0° to 180° and 𝜙 varies from 0° to 360°
-(such that any direction is possible). You can define the 𝜃 and 𝜙
-ranges with minimum and maximum values as follows:
-
-.. code:: python
-
-    source.direction.type = "iso"
-    source.direction.theta = [0, 10 * deg]
-    source.direction.phi = [0, 90 * deg]
-
-
 Geant4 defines the direction as: - x = -sin𝜃 cos𝜙; - y = -sin𝜃 sin𝜙; - z
 = -cos𝜃.