Remove duplicate Python version declarations

ruff can automatically detect this [1] now that it is defined in
pyproject.toml. mypy defaults to the version of Python used to run mypy
[2][3] so we need to keep its configuration around a while longer.

[1] https://docs.astral.sh/ruff/settings/#target-version
[2] https://mypy.readthedocs.io/en/stable/config_file.html#confval-python_version
[3] https://github.com/python/mypy/issues/19349

Change-Id: If5b3e6ff2483d73d5ff54cc28c1558cb9852b464
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>

pyproject.toml

@@ -742,7 +742,6 @@ ignore_errors = true
 
 [tool.ruff]
 line-length = 79
-target-version = "py310"
 
 [tool.ruff.format]
 quote-style = "preserve"