Revert unintential IAPI break for g_key_file_load_from_data()

Revert unintential IAPI break for g_key_file_load_from_data()

The old (length) annotation actually wasn't being read.  Changing
it to an array was telling g-i that it was an array of utf8, which
is clearly not true.

We *could* add (element-type guint8), but that would change it to a
byte array, as opposed to the original utf8 version.

Just removing the annotation should bring us back to where we
were, which was fine.

https://bugzilla.gnome.org/show_bug.cgi?id=680310