Revert "Merge pull request #39304 from zenspider/zenspider/backtrace_filter_should_never_return_empty"

This reverts commit 2eb7aa11, reversing
changes made to 0b28f0c3.

Rails backtrace cleaner needs to be able to return empty traces to
separate application code from the framework code and not report
exceptions that happen inside only framework code.

See
https://github.com/rails/rails/blob/345de17caf82f215b2a9a94e80eabf2473177e3a/actionpack/lib/action_dispatch/middleware/exception_wrapper.rb#L72.