Remove logo (pytest-dev#653)

Remove the dice logo. It's incompatible with the `twine check` run by
the new automated release from pytest-dev#652, and anyway, it's not very good.

Fail:
https://github.com/pytest-dev/pytest-randomly/actions/runs/11521126660/job/32074107912

Author: adamchainz

README.rst

@@ -18,10 +18,6 @@ pytest-randomly
    :target: https://github.com/pre-commit/pre-commit
    :alt: pre-commit
 
-.. figure:: https://raw.githubusercontent.com/pytest-dev/pytest-randomly/main/logo.png
-   :scale: 50%
-   :alt: Randomness power.
-
 Pytest plugin to randomly order tests and control ``random.seed``.
 
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