fix(popup): allow killing popup buffers

Currently, `SPC b k` does not allow us to kill popup buffers. If we are
say using a comint/eshell/eat buffer and we borked the state while
testing hooks or we sent EOF to the underlying process, our intention
with `SPC b k` is to kill the underlying buffer.

lisp/doom-ui.el

@@ -210,10 +210,7 @@ windows, switch to `doom-fallback-buffer'. Otherwise, delegate to original
 `kill-current-buffer'."
   :before-until #'kill-current-buffer
   (let ((buf (current-buffer)))
-    (cond ((window-dedicated-p)
-           (delete-window)
-           t)
-          ((eq buf (doom-fallback-buffer))
+    (cond ((eq buf (doom-fallback-buffer))
            (message "Can't kill the fallback buffer.")
            t)
           ((doom-real-buffer-p buf)