docs: Get rid of old LaTeX documentation (#1970)

Only use markdown -> readthedocs for the language specification.  No
need to continue maintaining the LaTeX version, it only makes it
confusing for people who don't know which they should be updating.

Signed-off-by: Larry Gritz <[email protected]>

Author: lgritz

src/doc/CMakeLists.txt

@@ -2,7 +2,7 @@
 # SPDX-License-Identifier: BSD-3-Clause
 # https://github.com/AcademySoftwareFoundation/OpenShadingLanguage
 
-set (public_docs osl-languagespec.pdf
+set (public_docs 
                  testshade.md.html
                  osltoy.md.html
                  markdeep.min.js