Allow packaging factory images from a separate bootloader file

Change-Id: Iffdf98cb424b4f7e82cd231395d736e572ae453d
diff --git a/clear-factory-images-variables.sh b/clear-factory-images-variables.sh
index 5528938..312f195 100644
--- a/clear-factory-images-variables.sh
+++ b/clear-factory-images-variables.sh
@@ -13,6 +13,7 @@
 # limitations under the License.
 
 unset BOOTLOADER
+unset BOOTLOADERFILE
 unset BOOTLOADERSRC
 unset BUILD
 unset CDMARADIO