Remove mention of selftest.qrc from generator script's doc

This supplements b1945604a7, which
removed the qrc file in favor of test/test.pro coding for it.

Change-Id: I15507c89ca14fa6e6b8223de671ffff7092272d0
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

tests/auto/testlib/selftests/generate_expected_output.py

@@ -37,9 +37,7 @@
 # it to the output of each test, ignoring various boring changes.
 # This script canonicalises the parts that would exhibit those boring
 # changes, so as to avoid noise in git (and conflicts in merges) for
-# the saved copies of the output.  If you add or remove any files, be
-# sure to update selftests.qrc to match; the selftest only sees files
-# listed there.
+# the saved copies of the output.
 
 import os
 import subprocess