Remove additional faces from trimesh.creation.revolve output

[lucagrementieri]

The function trimesh.creation.revolve produces an additional set of faces linking the points at the beginning and at the end of the provided line.

For example running this snippet, the assertion fails because 48 faces are produced, i.e. 2*sections more than the expected number

import trimesh.creation
import numpy as np

line = np.array([[1.0, 0.0], [1.0, 1.0], [1.0, 2.0], [1.0, 3.0]])
t = trimesh.creation.revolve(line, cap=False, sections=6)
assert t.vertices.shape == (24, 3)
assert t.faces.shape == (36, 3)

Viewing the mesh in MeshLab we can notice the presence of problematic faces.

This PR fixes the problem by avoiding the creation of the spurious faces, recovering the expected result.

[mikedh]

Thanks for the PR fix makes sense! It seems like we should have caught that somewhere in tests, although on quick inspection the area for a cylinder was coming out correctly with the prior logic?