Migrate search.cpan.org home pages to metacpan.org.

The venerable search.cpan.org has retired[0].

[0]: https://log.perl.org/2018/05/goodbye-search-dot-cpan-dot-org.html

* guix/import/cpan.scm (cpan-home): Generate metacpan.org home page URIs.
Update all previously generated ones in (gnu packages) to their
canonical new homes.

gnu/packages/freedesktop.scm

@@ -1179,7 +1179,7 @@ manually by a user.")
        ("xdg-user-dirs" ,xdg-user-dirs)))
     (propagated-inputs
      `(("perl-ipc-system-simple" ,perl-ipc-system-simple)))
-    (home-page "http://search.cpan.org/dist/File-BaseDir/")
+    (home-page "https://metacpan.org/release/File-BaseDir")
     (synopsis "Use the Freedesktop.org base directory specification")
     (description
      "@code{File::Basedir} can be used to find directories and files as
@@ -1207,7 +1207,7 @@ application data and cache data.")
     (propagated-inputs
      `(("perl-file-basedir" ,perl-file-basedir)
        ("perl-uri" ,perl-uri)))
-    (home-page "http://search.cpan.org/~michielb/File-DesktopEntry/")
+    (home-page "https://metacpan.org/release/File-DesktopEntry")
     (synopsis "Handle @file{.desktop} files")
     (description
      "@code{File::DesktopEntry} parses @file{.desktop} files defined by the
@@ -1249,7 +1249,7 @@ applications define in those files.")
                                                 "/lib/perl5/site_perl")))))
                          '("mimeopen" "mimetype")))
              #t)))))
-    (home-page "http://search.cpan.org/dist/File-MimeInfo/")
+    (home-page "https://metacpan.org/release/File-MimeInfo")
     (synopsis "Determine file type from the file name")
     (description
      "@code{File::Mimeinfo} can be used to determine the MIME type of a file.