A fix for a build error

The authorized_keys file may (for quite old out/ directories) be a
symlink to the identity file. This cleans up authorized_keys before
recreating it.

Change-Id: Ibe70a2459370dfaf6d935156b5bc1872f1b5d586
diff --git a/fuchsia/developer-keys/concat_authorized_keys.sh b/fuchsia/developer-keys/concat_authorized_keys.sh
index e21771a..b23dd43 100755
--- a/fuchsia/developer-keys/concat_authorized_keys.sh
+++ b/fuchsia/developer-keys/concat_authorized_keys.sh
@@ -7,4 +7,6 @@
   exit 1
 fi
 
-cat "${@:2}" > $1
+rm -f "$1"
+
+cat "${@:2}" > "$1"