gnu: python-sgp4: Move to astronomy.

* gnu/packages/astronomy.scm: (python-sgp4): Move here from python-science.scm.
  [description]: Expand description, annotate acronyms, add link to CelesTrak.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

gnu/packages/python-science.scm

@@ -290,26 +290,6 @@ logic, also known as grey logic.")
 genetic variation data.")
     (license license:expat)))
 
-(define-public python-sgp4
-  (package
-    (name "python-sgp4")
-    (version "2.21")
-    (source
-     (origin
-       (method url-fetch)
-       (uri (pypi-uri "sgp4" version))
-       (sha256
-        (base32 "1vzcrlrlzmhbycdz16m8v241l8zx49vsy81wcd0yjxs80isvhyb1"))))
-    (build-system python-build-system)
-    (propagated-inputs
-     (list python-numpy))
-    (home-page "https://github.com/brandon-rhodes/python-sgp4")
-    (synopsis "Track earth satellite TLE orbits using SGP4")
-    (description
-     "This package provides a Python implementation of the most recent version
-of the SGP4 satellite tracking algorithm.")
-    (license license:expat)))
-
 (define-public python-trimesh
   (package
     (name "python-trimesh")