C#: Address review comment from previous PR.

csharp/ql/integration-tests/all-platforms/dotnet_build/test.py

@@ -1,7 +1,6 @@
 import os
 
 def check_build_out(msg, s):
-    lines = s.splitlines()
     lines = s.splitlines()
     assert (
         any (("[build-stdout]" in line) and (msg in line) for line in lines)