gnu: parfive: Renamve variable.

The most of the time Parfive is used as Python's library which
complicates using Guix import, this change align the name with expected
by importer.

* gnu/packages/python-web.scm (parfive): Rename variable to python-parfive.
* gnu/packages/astronomy.scm (python-sunpy, python-sunpy-minimal)
[propagated-inputs]: Remove parfive; add python-parfive.

Change-Id: I1a6d29f64d9aa49caff2838125f0ee2ca0e65b46

gnu/packages/python-web.scm

@@ -2338,9 +2338,9 @@ HTTP servers, RESTful APIs, and web services.")
     (properties `((lint-hidden-cve . ("CVE-2019-10751"))))
     (license license:bsd-3)))
 
-(define-public parfive
+(define-public python-parfive
   (package
-    (name "parfive")
+    (name "python-parfive")
     (version "2.2.0")
     (source
      (origin