common: Fix creation of Windows socket directories.

* common/homedir.c (w32_try_mkdir): Remove.
(standard_homedir): Use gnupg_mkdir instead of w32_try_mkdir.
(_gnupg_socketdir_internal): Ditto.

The w32_try_mkdir was once introduced for WindowsCE and unfortunately
at a too brief inspection it looks like it does the utf8->wchar
conversion. Which it does not. Thus I obviously never tested the
switch to from APPDATA to LOCAL_APPDATA with a non-ascii account name.
That might have been due to the use of the very same code for the
homedir - but there is other code in gpg to create the homedir; thus a
failure here is mostly fixed later.

The missing error diagnostic was - and is - on purpose to avoid such
error messages due to a race between several running gpg instances.

• GnuPG-bug-id: T5537