Is there a way to DELETE apex classes and triggers? I don't want to just inactivate them

I have a text field that could contain text like:
"Please consult the related form [15dr4] for details"

But I'm trying to create a separate formula field that will hide the "15dr4" or whatever text is between the two brackets, but display the rest of the text.l Is this possible?

I appreciate any help. Thanks!