tools: docker: Drop patman from the CI image

The CI runner image pre-caches pip packages by downloading each tool's
requirements.txt from master. A later patch removes patman's
requirements.txt from the tree, so stop fetching and installing it.

The same step already installs setuptools explicitly (patman's
requirements list it too), so this needs nothing further.

This takes effect the next time someone rebuilds the image; the existing
image keeps working in the meantime.

Signed-off-by: Simon Glass <sjg@chromium.org>