Revert "gnu: libtasn1: Update to 4.6."

Causes a test of GnuTLS to fail:
<http://lists.gnu.org/archive/html/help-libtasn1/2015-09/msg00003.html>.

This reverts commit 866ee34f7e.

gnu/packages/tls.scm

@@ -40,7 +40,7 @@
 (define-public libtasn1
   (package
     (name "libtasn1")
-    (version "4.6")
+    (version "4.5")
     (source
      (origin
       (method url-fetch)
@@ -48,7 +48,7 @@
                           version ".tar.gz"))
       (sha256
        (base32
-        "12shiqjmck2g0rg57vr73dhy58kbwgsjb24sqdw6hlyjw8jzqqil"))))
+        "1nhvnznhg2aqfrfjxc8v008hjlzkh5831jsfahqk89qrw7fbbcw9"))))
     (build-system gnu-build-system)
     (native-inputs `(("perl" ,perl)