Don't wipe all of output/, only data TXZs

Otherwise we wipe source tarballs created by the build script.

release_builder/create_base_package.sh

@@ -24,11 +24,13 @@ cd $WORKSPACE
 
 
 # wipe directories and re-create
-rm -rf output
 rm -rf staging
 mkdir -p output
 mkdir -p staging
 
+# wipe existing data TXZs
+rm output/FlightGear-$VERSION*data.txz
+
 rsync -az --exclude=".git" fgdata staging/
 
 # add all the scenery pack files into it