Tweaks per review

Author: WardBrian

src/functions-reference/removed_functions.Rmd

@@ -2,3 +2,5 @@
 
 Functions which once existed in the Stan language and have since been replaced
 or removed will be listed here.
+
+As of the current version of Stan, there are no such functions.

src/reference-manual/deprecations.Rmd

@@ -10,7 +10,7 @@ Stan 2.23 and placed in [Removed Features]. The Stan compiler can
 many of these on the behalf of the user.
 
 Any feature which changes semantic meaning (such as the upgraded ODE solver
-interface) will not be removed until a major version change (e.g. Stan 3.0).
+interface) will not be removed until a major version change (e.g., Stan 3.0).
 
 
 ## Assignment with `<-`