buildscript: drop md5 checksum

The md5 checksum has not been used by fff-upgrade since 2016 [1]. Since
md5 does not have any advantages over sha256 in our use case, drop md5
checksum entirely.

[1] da1199a55b

Signed-off-by: Fabian Bläse <fabian@blaese.de>
Reviewed-by: Christian Dresel <freifunk@dresel.systems>

buildscript

@@ -313,7 +313,6 @@ buildrelease() {
 
     cd bin/$variant
     for binary in *.bin *.img *.img.gz *.tar; do
-        md5sum "$binary" > ./"$binary".md5
         sha256sum "$binary" > ./"$binary".sha256
     done
     echo -e "VERSION:$version" > release.nfo