lang/cc: remove +irony and +rtags flags from docs

They were removed a while back. Irony and rtags (et co) will be disabled
if +lsp is enabled, or can be disabled through package! declarations:

  ;; in ~/.doom.d/packages.el
  (package! irony :disable t)
  (package! rtags :disable t)

init.example.el

@@ -90,7 +90,7 @@
        :lang
        ;;agda              ; types of types of types of types...
        ;;assembly          ; assembly for fun or debugging
-       ;;(cc +irony +rtags); C/C++/Obj-C madness
+       ;;cc                ; C/C++/Obj-C madness
        ;;clojure           ; java with a lisp
        ;;common-lisp       ; if you've seen one lisp, you've seen them all
        ;;coq               ; proofs-as-programs