selectrum: improve :tools lookup integration

- move `consult-xref` stuff to `:tools lookup` where it belongs
- add selectrum functionality where possible, document what's beyond the
  scope of this PR

modules/completion/selectrum/TODO.org

@@ -6,6 +6,8 @@
 ** TODO =SPC s s= and =SPC s S= ~:sw~ ?
 There isn't really a selectrum analogue to ~swiper-isearch~, ~consult-isearch~
 does something else (give you previously used isearch search terms).
+** TODO =SPC s B=
+Selectrum/Consult don't have a ~swiper-all~ analogue either.
 
 * PROJ Bugs
 ** TODO =C-SPC= and live previews
@@ -38,7 +40,9 @@ main dispatch function like =ivy-bibtex=, rather it has a bunch of different
 ones. Binding the ~bibtex-actions-map~ there would probably be better, but there
 are nontrivial loading order shenanigans happening that make that not straightforward.
 ** TODO Ivy Parity
-*** TODO lookup module
-*** TODO taskrunner module (doesn't seem to be an interface yet)
-*** TODO pass module (creating embark-pass can't be that hard)
-*** TODO =SPC s B= (~swiper-all~ analogue)
+*** TODO pass module
+*** WAIT lookup module
+- ~dash-docs~ backend (needs to be created)
+- ~+lookup--online..~ functionality (needs a consult analogue of ~counsel-search~)
+*** WAIT taskrunner module
+in all likelihood requires writing ~consult-taskrunner~.

modules/completion/selectrum/config.el

@@ -100,12 +100,6 @@
   (setq consult-async-input-debounce 0.5)
   (setq consult-async-input-throttle 0.8))
 
-(use-package! consult-xref
-  :defer t
-  :init
-  (setq xref-show-xrefs-function       #'consult-xref
-        xref-show-definitions-function #'consult-xref))
-
 (use-package! consult-flycheck
   :when (featurep! :checkers syntax)
   :after (consult flycheck))