guix: Remove unused file package

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

contrib/guix/libexec/build.sh

@@ -137,8 +137,7 @@ export GUIX_LD_WRAPPER_DISABLE_RPATH=yes
 # Make /usr/bin if it doesn't exist
 [ -e /usr/bin ] || mkdir -p /usr/bin
 
-# Symlink file and env to a conventional path
-[ -e /usr/bin/file ] || ln -s --no-dereference "$(command -v file)" /usr/bin/file
+# Symlink env to a conventional path
 [ -e /usr/bin/env ]  || ln -s --no-dereference "$(command -v env)"  /usr/bin/env
 
 # Determine the correct value for -Wl,--dynamic-linker for the current $HOST