gnu: cross-base: Remove unneeded 'let'.

This is a followup to 102d307520dee27a40feb1ca5a699763a2f3aefe.

* gnu/packages/cross-base.scm (cross-libc): Remove (let ((libc libc)) …).

gnu/packages/cross-base.scm

@@ -469,8 +469,8 @@ and the cross tool chain."
       (native-libc target libc
                    #:xgcc xgcc
                    #:xbinutils xbinutils)
-      (let ((libc libc))
-        (package (inherit libc)
+      (package
+        (inherit libc)
         (name (string-append "glibc-cross-" target))
         (arguments
          (substitute-keyword-arguments
@@ -531,7 +531,7 @@ and the cross tool chain."
                                                "cross-mig")))
                                '())
                          ,@(package-inputs libc)  ;FIXME: static-bash
-                           ,@(package-native-inputs libc)))))))
+                         ,@(package-native-inputs libc))))))
 
 (define* (native-libc target
                      #:optional