libffi: remove unneeded build workaround

extra/libffi/build

@@ -1,18 +1,5 @@
 #!/bin/sh -e
 
-# If 'file' is not available, mimic the output
-# required for KISS.
-mkdir -p fakebin
-cat > fakebin/file <<EOF
-#!/bin/sh
-echo 64-bit
-EOF
-chmod +x fakebin/file
-export PATH=$PATH:$PWD/fakebin
-
-# Use 'file' from '$PATH'.
-sed -i'' "s|/usr/bin/file|file|g" configure
-
 ./configure \
     --prefix=/usr \
     --with-pic