vendor.sh: clean out 7ztest on startup

otherwise, some files from a previous me.bin scan
might still be there, which could lead to the wrong
me.bin being found.

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

include/vendor.sh

@@ -148,6 +148,7 @@ extract_intel_me()
 	_7ztest="$xbtmp/metmp/a"
 	_metmp="$xbtmp/me.bin"
 	x_ rm -f "$_metmp" "$xbtmp/a"
+	x_ rm -Rf "$_7ztest"
 
 	mfs=""
 	if [ "$ME11bootguard" = "y" ]; then