gnu: Remove go-github-com-tj-docopt.

It's a not maintained (10y) fork of
<https://github.com/docopt/docopt.go>, fails to build and not in use by
any other packages in Guix.

* gnu/packages/golang.scm (go-github-com-tj-docopt): Delete variable.

Change-Id: I356cd0250fe246a300ac2e6cd31255552cf95675

gnu/packages/golang.scm

@@ -2523,30 +2523,6 @@ per-goroutine.")
     (description "The @code{walker} function is a faster, parallel version, of
 @code{filepath.Walk}")))
 
-(define-public go-github-com-tj-docopt
-  (package
-    (name "go-github-com-tj-docopt")
-    (version "1.0.0")
-    (source (origin
-              (method git-fetch)
-              (uri (git-reference
-                    (url "https://github.com/tj/docopt")
-                    (commit (string-append "v" version))))
-              (file-name (git-file-name name version))
-              (sha256
-               (base32
-                "06h8hdg1mh3s78zqlr01g4si7k0f0g6pr7fj7lnvfg446hgc7080"))))
-    (build-system go-build-system)
-    (arguments
-     '(#:import-path "github.com/tj/docopt"))
-    (synopsis "Go implementation of docopt")
-    (description
-     "This library allows the user to define a command-line interface from a
-program's help message rather than specifying it programmatically with
-command-line parsers.")
-    (home-page "https://github.com/tj/docopt")
-    (license license:expat)))
-
 (define-public gopls
   (package
     (name "gopls")