We don't need this anymore: Win32 doesn't use this library at all, and
everything else has either iconv() or libicu.

default_value defaults to nullptr.

Since we are removing GLib, this call is useless.

I suppose there is no non-WIN32 operating system that doesn't have
fnmatch().  So let's remove the GLib implementation.

Drop support for misencoded tags.  People should not be using ID3v1
anyway.

The default is always UTF-8.

Always write UTF-8 to the log file.

Don't define HAVE_FS_CHARSET, and make GetFSCharset() return "ACP"
instead of "UTF-8".  Ignore the configuration setting, which had no
effect anyway.