remove msys2 and app engine detection (#2554)

CHANGES.rst

@@ -28,6 +28,8 @@ Unreleased
     ``cls`` parameter is used. :issue:`2294`
 -   Don't fail when writing filenames to streams with strict errors. Replace invalid
     bytes with the replacement character (``�``). :issue:`2395`
+-   Remove unnecessary attempt to detect MSYS2 environment. :issue:`2355`
+-   Remove outdated and unnecessary detection of App Engine environment. :pr:`2554`
 
 
 Version 8.1.3

src/click/_compat.py

@@ -7,12 +7,7 @@
 from weakref import WeakKeyDictionary
 
 CYGWIN = sys.platform.startswith("cygwin")
-MSYS2 = sys.platform.startswith("win") and ("GCC" in sys.version)
-# Determine local App Engine environment, per Google's own suggestion
-APP_ENGINE = "APPENGINE_RUNTIME" in os.environ and "Development/" in os.environ.get(
-    "SERVER_SOFTWARE", ""
-)
-WIN = sys.platform.startswith("win") and not APP_ENGINE and not MSYS2
+WIN = sys.platform.startswith("win")
 auto_wrap_for_ansi: t.Optional[t.Callable[[t.TextIO], t.TextIO]] = None
 _ansi_re = re.compile(r"\033\[[;?0-9]*[a-zA-Z]")