Drop mypy self test (#5344)

Closes: #5303

tests/mypy_self_check.py

@@ -1,55 +0,0 @@
-#!/usr/bin/env python3
-"""Script to run mypy against its own code base."""
-
-import os
-import re
-import subprocess
-import sys
-import tempfile
-from pathlib import Path
-
-REQUIREMENTS_FILE = "requirements-tests-py3.txt"
-MYPY_REQUIREMENTS_REGEXPS = [r"^mypy[ =>]", r"^git\+.*/mypy.git\W"]
-
-
-def determine_mypy_version() -> str:
-    with open(REQUIREMENTS_FILE) as f:
-        for line in f:
-            for regexp in MYPY_REQUIREMENTS_REGEXPS:
-                m = re.match(regexp, line)
-                if m:
-                    return line.strip()
-    raise RuntimeError(f"no mypy version found in {REQUIREMENTS_FILE}")
-
-
-if __name__ == "__main__":
-    mypy_version = determine_mypy_version()
-
-    with tempfile.TemporaryDirectory() as tempdir:
-        dirpath = Path(tempdir)
-        subprocess.run(
-            ["git", "clone", "--depth", "1", "git://github.com/python/mypy", dirpath],
-            check=True,
-        )
-        os.environ["MYPYPATH"] = str(dirpath)
-        try:
-            subprocess.run([sys.executable, "-m", "pip", "install", "-U", mypy_version], check=True)
-            subprocess.run([sys.executable, "-m", "pip", "install", "-r", dirpath / "test-requirements.txt"], check=True)
-            subprocess.run(
-                [
-                    "mypy",
-                    "--config-file",
-                    dirpath / "mypy_self_check.ini",
-                    "--custom-typeshed-dir",
-                    ".",
-                    "-p", "mypy",
-                    "-p", "mypyc",
-                ],
-                check=True,
-            )
-        except subprocess.CalledProcessError as e:
-            print("mypy self test failed", file=sys.stderr)
-            sys.exit(e.returncode)
-        else:
-            print("mypy self test succeeded", file=sys.stderr)
-            sys.exit(0)