gnu: Remove ‘open source’ from package descriptions.

Also do some (trivial) editing where appropriate.

* gnu/packages/bioconductor.scm (r-anaquin, r-rcppnumerical)
[description]: Remove superfluous ‘open source’.
* gnu/packages/debian.scm (apt-mirror)[description]: Likewise.
Add @acronym{}.  Drop obscure Ubuntu for famous Trisquel.  Reorder.
* gnu/packages/documentation.scm (scrollkeeper)[description]:
Remove superfluous ‘open systems’.  Keep ‘Open Source’ in standard name.
* gnu/packages/engineering.scm (freecad, cura-engine)[description]:
Remove superfluous ‘open source’ and excessive puffery.
* gnu/packages/firmware.scm (make-opensbi-package)
[synopsis]: Remove ‘Open Source’.  Use @acronym{}.
[description]: Fix first sentence to follow guidelines.  Use @acronym{}.
* gnu/packages/game-development.scm (ioquake3, recastnavigation):
[description]: Remove ‘open source’.
* gnu/packages/graphics.scm (skia)[description]: Likewise.
* gnu/packages/lisp-xyz.scm (sbcl-s-sysdeps)[description]: Likewise.
* gnu/packages/machine-learning.scm (onnx)[description]: Likewise.
Use @acronym{}.
* gnu/packages/ocaml.scm (ocaml-cudf)[description]: Likewise.

gnu/packages/lisp-xyz.scm

@@ -6831,7 +6831,7 @@ extension-points via the concept of hooks.")
       (synopsis "Common Lisp abstraction layer over platform dependent functionality")
       (description "@code{s-sysdeps} is an abstraction layer over platform
 dependent functionality.  This simple package is used as a building block in a
-number of other open source projects.
+number of other projects.
 
 @code{s-sysdeps} abstracts: