Stop mentioning wheel in the context of PEP 517

This dependency is exposed automatically by setuptools and the users
do not need to declare it explicitly — it will be installed by
PEP 517 front-ends automatically, when building wheels.

Author: webknjaz

docs/build_meta.rst

@@ -53,12 +53,13 @@ being used to package your scripts and install from source). To use it with
 setuptools, the content would be::
 
     [build-system]
-    requires = ["setuptools", "wheel"]
+    requires = ["setuptools"]
     build-backend = "setuptools.build_meta"
 
 The ``setuptools`` package implements the ``build_sdist``
 command and the ``wheel`` package implements the ``build_wheel``
-command; both are required to be compliant with PEP 517.
+command; the latter is a dependency of the former
+exposed via :pep:`517` hooks.
 
 Use ``setuptools``' :ref:`declarative config <declarative config>` to
 specify the package information::

docs/userguide/dependency_management.rst

@@ -28,7 +28,7 @@ other two types of dependency keyword, this one is specified in your
 .. code-block:: ini
 
     [build-system]
-    requires = ["setuptools", "wheel"]
+    requires = ["setuptools"]
     #...
 
 .. note::

docs/userguide/quickstart.rst

@@ -32,7 +32,7 @@ package your project:
 .. code-block:: toml
 
     [build-system]
-    requires = ["setuptools", "wheel"]
+    requires = ["setuptools"]
     build-backend = "setuptools.build_meta"
 
 Then, you will need a ``setup.cfg`` or ``setup.py`` to specify your package