xbmk: reintroduce setvar as newvar (init only)

use the simpler logic recently introduced, generalised
but it only sets variables to empty. this is safer than
the previous design, and brings the same reduction in
sloccount overall since i wasn't doing anything other
than emptying variables anyway, when it was used before.

i didn't like the long list of variables inside files,
so this makes everything more readable.

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

include/get.sh

@@ -3,16 +3,8 @@
 # Copyright (c) 2020-2021,2023-2026 Leah Rowe <leah@libreboot.org>
 # Copyright (c) 2022 Caleb La Grange <thonkpeasant@protonmail.com>
 
-url=""
-bkup_url=""
-
-depend=""
-loc=""
-subcurl=""
-subcurl_bkup=""
-subgit=""
-subgit_bkup=""
-subhash=""
+eval "`newvar url bkup_url depend loc subcurl subcurl_bkup subgit subgit_bkup \
+    subhash`"
 
 tmpgit="$xbtmp/gitclone"
 tmpgitcache="$xbtmp/tmpgit"