PyAPI: remove deprecated 2D_/3D_ prefix for built-in shader names

Names passed to gpu.shader.from_builtin()
no longer skip the 2D_/3D_ prefix.

doc/python_api/examples/gpu.5.py

@@ -13,7 +13,7 @@ vertices = (
 indices = (
     (0, 1, 2), (2, 1, 3))
 
-shader = gpu.shader.from_builtin('2D_UNIFORM_COLOR')
+shader = gpu.shader.from_builtin('UNIFORM_COLOR')
 batch = batch_for_shader(shader, 'TRIS', {"pos": vertices}, indices=indices)