Remove linked app from links file when destroying app

tests/test_helper.bash

@@ -10,6 +10,7 @@ export PLUGIN_AVAILABLE_PATH="$PLUGIN_PATH"
 export PLUGIN_CORE_AVAILABLE_PATH="$PLUGIN_PATH"
 export POSTGRES_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)/fixtures"
 export PLUGIN_DATA_ROOT="$POSTGRES_ROOT"
+export PLUGN_URL="https://github.com/progrium/plugn/releases/download/v0.1.0/plugn_0.1.0_linux_x86_64.tgz"
 
 mkdir -p "$PLUGIN_DATA_ROOT"
 rm -rf "${PLUGIN_DATA_ROOT:?}"/*