docs: document only the IDS theme, drop stock reveal.js themes

Change-Id: I379e9fc0b46a42841eef96f17536b4c498334323
diff --git a/R/revealjs_presentation.R b/R/revealjs_presentation.R
index fa31dca..ec8a814 100644
--- a/R/revealjs_presentation.R
+++ b/R/revealjs_presentation.R
@@ -169,11 +169,8 @@
 #'   produced, with level 1 headers building horizontally and level 2 headers
 #'   building vertically. It is not recommended that you use deeper nesting of
 #'   section levels with reveal.js.
-#' @param theme Visual theme. Defaults to the dedicated IDS corporate design
-#'   theme ("ids"), which is the raison d'être of this package; the stock
-#'   reveal.js themes are available as rarely used alternatives:
-#'   `r knitr::combine_words(setdiff(revealjs_themes(), c("default", "ids")), before = '"', and = " or ")`
-#'   ("dark" is an alias for "black").
+#' @param theme Visual theme. The dedicated IDS corporate design theme
+#'   ("ids") is the default and the only supported theme.
 #' @param transition Slide transition (
 #' `r (trans <- knitr::combine_words(setdiff(revealjs_transitions(), "default"), before = '"', and = " or "))`
 #' )