Remove line number filtering

Remove `--line-number` option.

CLI filtering options are meant to globally apply
but `--line-number` really only makes sense in the
context of a particular file.

rspec path/to/spec.rb:12:23 is a better way to
filter to an example based on the line.

Fixes #1243 and paves the way for #952.

Note: I still need to add a 2.99 deprecation.