guix: Remove unused file package

The `file` utility has not been required since Guix builds were
introduced.

contrib/guix/manifest.scm

@@ -6,7 +6,6 @@
              (gnu packages commencement)
              (gnu packages compression)
              (gnu packages cross-base)
-             (gnu packages file)
              (gnu packages gawk)
              (gnu packages gcc)
              ((gnu packages installers) #:select (nsis-x86_64))
@@ -531,7 +530,6 @@ inspecting signatures in Mach-O binaries.")
         which
         coreutils-minimal
         ;; File(system) inspection
-        file
         grep
         diffutils
         findutils