gnu: libssh2@1.8.0: Move to ssh.scm.

This fixes a top-level circular dependency introduced in
c1f4e6491c.

* gnu/packages/curl.scm (libssh2-1.8.0): Move to...
* gnu/packages/ssh.scm (libssh2-1.8.0): ... here.

gnu/packages/curl.scm

@@ -48,24 +48,6 @@ (define-module (gnu packages curl)
   #:use-module (gnu packages tls)
   #:use-module (gnu packages web))
 
-;; XXX A hidden special obsolete libssh2 for temporary use in the curl package.
-;; <https://bugs.gnu.org/34927>
-(define-public libssh2-1.8.0
-  (hidden-package
-    (package
-      (inherit libssh2)
-      (version "1.8.0")
-      (source (origin
-                (method url-fetch)
-                (uri (string-append
-                      "https://www.libssh2.org/download/libssh2-"
-                      version ".tar.gz"))
-                (sha256
-                 (base32
-                  "1m3n8spv79qhjq4yi0wgly5s5rc8783jb1pyra9bkx1md0plxwrr"))
-                (patches
-                 (search-patches "libssh2-fix-build-failure-with-gcrypt.patch")))))))
-
 (define-public curl
   (package
    (name "curl")

gnu/packages/ssh.scm

@@ -143,6 +143,24 @@ (define-public libssh2
    (license license:bsd-3)
    (home-page "https://www.libssh2.org/")))
 
+;; XXX A hidden special obsolete libssh2 for temporary use in the curl package.
+;; <https://bugs.gnu.org/34927>
+(define-public libssh2-1.8.0
+  (hidden-package
+    (package
+      (inherit libssh2)
+      (version "1.8.0")
+      (source (origin
+                (method url-fetch)
+                (uri (string-append
+                      "https://www.libssh2.org/download/libssh2-"
+                      version ".tar.gz"))
+                (sha256
+                 (base32
+                  "1m3n8spv79qhjq4yi0wgly5s5rc8783jb1pyra9bkx1md0plxwrr"))
+                (patches
+                 (search-patches "libssh2-fix-build-failure-with-gcrypt.patch")))))))
+
 (define-public openssh
   (package
    (name "openssh")