remove download scripts, consolidate into script

most of them were just calling the gitclone script,
so remove them.

the grub script was treating gnulib as a dependency.
i've now added the ability to grab 1 dependency, in
the gitclone script (it should be expanded later to
support multiple dependencies)

the gitclone script has been renamed to "fetch".
the "fetch_trees" script does more or less the same
thing, but calls "fetch" and handles multiple revisions
if a project needs that

this is more efficient, and slightly reduces the code
size of lbmk!

Signed-off-by: Leah Rowe <leah@libreboot.org>

lbmk

@@ -33,9 +33,6 @@ main()
 {
 	if [ "${0##*/}" = "lbmk" ]; then
 		die "Do not run the lbmk script directly!"
-	elif [ "${0##*/}" = "download" ]; then
-		./update module $@ || exit 1
-		exit 0
 	elif [ "${0##*/}" = "blobutil" ]; then
 		./update blobs $@ || exit 1
 		exit 0