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/init.sh

@@ -33,25 +33,9 @@ fi
 
 sha512sum="util/sbase/sha512sum"
 
-aur_notice=""
-basetmp=""
-board=""
-checkvarschk=""
-checkvarsxbmk=""
-configdir=""
-datadir=""
-is_child=""
-python=""
-pyver=""
-reinstall=""
-relname=""
-version=""
-versiondate=""
-xbmklock=""
-xbmkpath=""
-xbmkpwd=""
-xbmkpwd=""
-xbtmp=""
+eval "`newvar aur_notice basetmp board checkvarschk checkvarsxbmk configdir \
+    datadir is_child python pyver reinstall relname version versiondate \
+    xbmklock xbmkpath xbmkpwd xbmkpwd xbtmp`"
 
 xbmk_init()
 {