Replace HIDAPI license text with "original" license.

[icculus]

According to hidapi's repo, the license options are:

HIDAPI can be used under one of three licenses.

1. The GNU General Public License, version 3.0, in LICENSE-gpl3.txt
2. A BSD-Style License, in LICENSE-bsd.txt.
3. The more liberal original HIDAPI license. LICENSE-orig.txt

The license chosen is at the discretion of the user of HIDAPI. For example:

1. An author of GPL software would likely use HIDAPI under the terms of the
   GPL.

2. An author of commercial closed-source software would likely use HIDAPI
   under the terms of the BSD-style license or the original HIDAPI license.

The "original license" is:

HIDAPI - Multi-Platform library for
communication with HID devices.

Copyright 2009, Alan Ott, Signal 11 Software.
All Rights Reserved.

This software may be used by anyone for any reason so
long as the copyright notice in the source files
remains intact.

This is simpler than the BSD license, requiring less from users of the code, so we should replace this at the top of SDL_hidapi.h, but it's also completely compatible with the zlib license, as it's only requirement is the same as zlib's third point ("This notice may not be removed or altered from any source distribution."), which means no one would have to build with SDL_HIDAPI_DISABLED for licensing requirements.

[icculus]

(Putting this in 3.2.0, but we should do this to SDL2, also.)