bpo-41410: Fix outdated info in mkstemp docs (GH-21701)

Automerge-Triggered-By: @ericvsmith

Author: xrisk

Doc/library/tempfile.rst

@@ -175,9 +175,8 @@ The module defines the following user-callable items:
    If you want to force a bytes return value with otherwise default behavior,
    pass ``suffix=b''``.
 
-   If *text* is specified, it indicates whether to open the file in binary
-   mode (the default) or text mode.  On some platforms, this makes no
-   difference.
+   If *text* is specified and true, the file is opened in text mode.
+   Otherwise, (the default) the file is opened in binary mode.
 
    :func:`mkstemp` returns a tuple containing an OS-level handle to an open
    file (as would be returned by :func:`os.open`) and the absolute pathname

Lib/tempfile.py

@@ -308,8 +308,7 @@ def mkstemp(suffix=None, prefix=None, dir=None, text=False):
     otherwise a default directory is used.
 
     If 'text' is specified and true, the file is opened in text
-    mode.  Else (the default) the file is opened in binary mode.  On
-    some operating systems, this makes no difference.
+    mode.  Else (the default) the file is opened in binary mode.
 
     If any of 'suffix', 'prefix' and 'dir' are not None, they must be the
     same type.  If they are bytes, the returned name will be bytes; str