Stop converting package_data to extra_files in pysetup create (#13712).

pysetup create, the setup.cfg creation helper, used to convert
package_data (from an existing setup.py) into extra_files, the
replacement for MANIFEST.in, but these files are only present in sdists,
not installed: they don’t have the same use case at all, so converting
one into the other did not work.
diff --git a/Misc/NEWS b/Misc/NEWS
index 91972bf..41fc63e 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -466,6 +466,8 @@
 Library
 -------
 
+- Issue #13712: pysetup create should not convert package_data to extra_files.
+
 - Issue #11805: package_data in setup.cfg should allow more than one value.
 
 - Issue #13901: Prevent test_distutils failures on OS X with --enable-shared.