Revert "gnu: xorg-server: Make the test-variant visible."

Hiding/unhiding changes the derivation and thus this caused too many rebuilds
for 'master'.

This reverts commit 8cf892e6cd.

gnu/packages/xorg.scm

@@ -5213,7 +5213,10 @@ draggable titlebars and borders.")
     (license license:x11)))
 
 ;; This package is intended to be used when building GTK+.
+;; Note: It's currently marked as "hidden" to avoid having two non-eq?
+;; packages with the same name and version.
 (define-public xorg-server-1.19.3
+  (hidden-package
    (package
      (inherit xorg-server)
      (name "xorg-server")
@@ -5226,7 +5229,7 @@ draggable titlebars and borders.")
               name "-" version ".tar.bz2"))
         (sha256
          (base32
-         "162s1v901djr57gxmmk4airk8hiwcz79dqyz72972x1lw1k82yk7"))))))
+          "162s1v901djr57gxmmk4airk8hiwcz79dqyz72972x1lw1k82yk7")))))))
 
 (define-public xorg-server-xwayland
   (package