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>

resources/scripts/modify/seabios/configs

@@ -30,7 +30,7 @@ main()
 download_seabios()
 {
 	if [ ! -d "seabios" ]; then
-		./download seabios
+		./fetch seabios
 	fi
 	if [ ! -d "seabios" ]; then
 		printf "error: Failed to download SeaBIOS. "