tests: fix BadLogLines for "No such file" messages

This assert originally went in when we wanted to check
we weren't grepping on a nonexistent path, but it turns
out there are certain conditions under which Redpanda
can emit matching log messages, which we should be
handling as the usual BadLogLines, not asserting on.

tests/rptest/services/redpanda.py

@@ -1029,8 +1029,6 @@ def raise_on_bad_logs(self, allow_list=None):
             ):
                 line = line.strip()
 
-                assert "No such file or directory" not in line
-
                 allowed = False
                 for a in allow_list:
                     if a.search(line) is not None: