Remove redundant wheel dep from pyproject.toml (#375)

Remove the redundant `wheel` dependency, as it is added by the backend
automatically.  Listing it explicitly in the documentation was
a historical mistake and has been fixed since, see:
f7d30a9529

---------

Co-authored-by: Ashley Whetter <ashley@awhetter.co.uk>

docs/changes/375.misc.rst

@@ -0,0 +1 @@
+Remove redundant dependency on wheel

pyproject.toml

@@ -1,5 +1,5 @@
 [build-system]
-requires = ["setuptools>=46.4.0", "wheel"]
+requires = ["setuptools>=46.4.0"]
 build-backend = "setuptools.build_meta"
 
 [[tool.mypy.overrides]]