Remove obsolete test code in runtests.py

[diazona]

The script runtests.py contains an archive of a very old version of pytest along with a custom mechanism to import it. That used to be the standard method of running tests (so I hear, anyway), but now it's no longer relevant because we use tox for dependency management in testing. So I'm removing the script. Having a large opaque blob of data is not the greatest thing :-)

For future reference, if anyone reading this wants to find out what's in that opaque blob, you can apply this patch and then run runtests.py, and it will write out the enclosed Python code into the directory runtests/ so you can read it.

diff --git a/runtests.py b/runtests.py
index a985c37..ed7792f 100644
--- a/runtests.py
+++ b/runtests.py
@@ -2708,9 +2708,9 @@ if __name__ == "__main__":
 
     sources = sources.encode("ascii")  # ensure bytes
     sources = pickle.loads(zlib.decompress(base64.decodebytes(sources)))
-
-    importer = DictImporter(sources)
-    sys.meta_path.insert(0, importer)
-
-    entry = "import py; raise SystemExit(py.test.cmdline.main())"
-    do_exec(entry, locals())  # noqa: F821
+    import pathlib
+    for k, v in sources.items():
+        path = pathlib.Path("runtests/" + k.replace(".", "/") + ".py")
+        path.parent.mkdir(parents=True, exist_ok=True)
+        with path.open("w") as f:
+            f.write(v)