Top of my head, I am pretty sure that I can do that with a "keyboard macro" involving list-matching-lines, and delete-matching-lines (that is literally what the commands are called). "Keyboard macro" by the way is a good and a bad name at once: It does not fully describe the vastly more powerful feature, as it is much more semantic than just repetition of keystrokes, but at its surface it looks like that and helps you get started.

If anyone reading this hasn't used keyboard macros in emacs, try it out the next time you do something repetitive. It's amazing how it can simplify those tasks. "C-x (" to start defining one, "C-x )" to end it, "C-x e" to run it, which conveniently also ends definition if you want to use it right away. Of course you can do things like "M-5 C-x e" to run it 5 times.

But I do get your point: Things are probably much less discoverable in emacs, unless you are relatively proficient in it already maybe. You need to switching into a "programmer" mind fairly quickly, while BBedit probably just lets you do powerful stuff through simple UI.