Backend: further fixes for GSIs

- ro.vendor.build.product (from #44) doesn't appear to actually exist in nature, so replace it with ro.product.vendor.device for API 28+ devices, per https://github.com/phhusson/vendor_hardware_overlay/issues/25
- no need to check so many props for getprop parsing fallback check, simply look for ro.build.type which all devices should have in antiquity

META-INF/com/google/android/update-binary

@@ -173,7 +173,7 @@ if [ ! "$(getprop 2>/dev/null)" ]; then
     done;
     test "$propval" && echo "$propval" || echo "";
   }
-elif [ ! "$(getprop ro.product.device 2>/dev/null)" -a ! "$(getprop ro.build.product 2>/dev/null)" -a ! "$(getprop ro.vendor.product.device 2>/dev/null)" -a ! "$(getprop ro.vendor.build.product 2>/dev/null)" ]; then
+elif [ ! "$(getprop ro.build.type 2>/dev/null)" ]; then
   getprop() {
     ($(which getprop) | $bb grep "$1" | $bb cut -d[ -f3 | $bb cut -d] -f1) 2>/dev/null;
   }
@@ -183,8 +183,8 @@ if [ "$(file_getprop anykernel.sh do.devicecheck)" == 1 ]; then
   ui_print "Checking device...";
   device=$(getprop ro.product.device 2>/dev/null);
   product=$(getprop ro.build.product 2>/dev/null);
-  vendordevice=$(getprop ro.vendor.product.device 2>/dev/null);
-  vendorproduct=$(getprop ro.vendor.build.product 2>/dev/null);
+  vendordevice=$(getprop ro.product.vendor.device 2>/dev/null);
+  vendorproduct=$(getprop ro.vendor.product.device 2>/dev/null);
   for testname in $(file_getprop anykernel.sh 'device.name.*'); do
     for devicename in $device $product $vendordevice $vendorproduct; do
       if [ "$devicename" == "$testname" ]; then