gnu: rust-cfg-expr-0.8: Combine the two definitions.

* gnu/packages/crates-io.scm (rust-cfg-expr-0.8): Remove duplicate
package definition.
[arguments]: Don't skip tests. Add rust-difference-2 to
cargo-development-inputs.

gnu/packages/crates-io.scm

@@ -9048,10 +9048,11 @@ (define-public rust-cfg-expr-0.8
         (base32 "03lgv8psc2qrr93hxgdfmfwbj1crpzghxd7qh6w2nz0l4qryh4ml"))))
     (build-system cargo-build-system)
     (arguments
-     `(#:skip-build? #t
+     `(#:cargo-inputs
-       #:cargo-inputs
        (("rust-smallvec" ,rust-smallvec-1)
-        ("rust-target-lexicon" ,rust-target-lexicon-0.12))))
+        ("rust-target-lexicon" ,rust-target-lexicon-0.12))
+       #:cargo-development-inputs
+       (("rust-difference" ,rust-difference-2))))
     (home-page "https://github.com/EmbarkStudios/cfg-expr")
     (synopsis "Parser and evaluator for Rust @code{cfg()} expressions")
     (description
@@ -54766,30 +54767,6 @@ (define-public rust-syslog-3
     (description "Send log messages to syslog.")
     (license license:expat)))
 
-(define-public rust-cfg-expr-0.8
-  (package
-    (name "rust-cfg-expr")
-    (version "0.8.1")
-    (source
-     (origin
-       (method url-fetch)
-       (uri (crate-uri "cfg-expr" version))
-       (file-name (string-append name "-" version ".tar.gz"))
-       (sha256
-        (base32 "03lgv8psc2qrr93hxgdfmfwbj1crpzghxd7qh6w2nz0l4qryh4ml"))))
-    (build-system cargo-build-system)
-    (arguments
-     `(#:cargo-inputs
-       (("rust-smallvec" ,rust-smallvec-1)
-        ("rust-target-lexicon" ,rust-target-lexicon-0.12))
-       #:cargo-development-inputs
-       (("rust-difference" ,rust-difference-2))))
-    (home-page "https://github.com/EmbarkStudios/cfg-expr")
-    (synopsis "Parser and evaluator for Rust @samp{cfg} expressions")
-    (description "This package provides a parser and evaluator for Rust
-@samp{cfg} expressions.")
-    (license (list license:expat license:asl2.0))))
-
 (define-public rust-system-deps-3
   (package
     (name "rust-system-deps")