Specify exact BSD license for XSL style sheets

[robe]

As noted in ​https://lists.osgeo.org/pipermail/postgis-devel/2023-July/030035.html

THE licensing of our XSL sheets is unclear since there are several BSD licenses.

It should be explicitly stated that it is BSD-3-Clause and reference to the licensing.

[Regina Obe <lr@…>]

In 1a52581/git:

Clarify licensing of XSL style sheets

References #5449 for PostGIS 3.4.0

[Regina Obe <lr@…>]

In c336509/git:

Clarify licensing of XSL style sheets
References #5449 for PostGIS 3.3.4

[strk]

Anything else to do here Regina or can this be closed ?

[robe]

I think we are done.

[robe]

Oh wait I remember why I left this open, was to push back to 3.0. But I'm too lazy for that so will flip to 3.3.4