gnu: cURL: Remove graft for 7.74.0 and reinstate lost patch.

See <https://lists.gnu.org/archive/html/guix-devel/2020-12/msg00142.html> for
a discussion about the missing patch.

* gnu/packages/curl.scm (curl): Update to 7.74.0.
[replacement]: Remove.
[source](patches): New field.
(curl-7.74.0): Remove variable.

gnu/packages/curl.scm

@@ -53,15 +53,15 @@
 (define-public curl
   (package
    (name "curl")
-   (version "7.73.0")
-   (replacement curl-7.74.0)
+   (version "7.74.0")
    (source (origin
              (method url-fetch)
              (uri (string-append "https://curl.haxx.se/download/curl-"
                                  version ".tar.xz"))
              (sha256
               (base32
-               "12j0qaij1ppgspray8xvs2qk3h3m23wdqh27x87y1aw8xaj7qk3w"))))
+               "12w7gskrglg6qrmp822j37fmbr0icrcxv7rib1fy5xiw80n5z7cr"))
+             (patches (search-patches "curl-use-ssl-cert-env.patch"))))
    (build-system gnu-build-system)
    (outputs '("out"
               "doc"))                             ;1.2 MiB of man3 pages
@@ -151,19 +151,6 @@ tunneling, and so on.")
     (name "curl-minimal")
     (inputs (alist-delete "openldap" (package-inputs curl))))))
 
-;; Replacement package to fix multiple security vulnerabilities.
-(define curl-7.74.0
-  (package
-    (inherit curl)
-    (version "7.74.0")
-    (source (origin
-              (inherit (package-source curl))
-              (uri (string-append "https://curl.haxx.se/download/curl-"
-                                  version ".tar.xz"))
-              (sha256
-               (base32
-                "12w7gskrglg6qrmp822j37fmbr0icrcxv7rib1fy5xiw80n5z7cr"))))))
-
 (define-public kurly
   (package
     (name "kurly")