Deprecate original API

Author: latkin

src/fsharp/vs/service.fsi

@@ -260,6 +260,7 @@ type FSharpCheckFileResults =
     member GetExtraColorizationsAlternate : unit -> (range * FSharpTokenColorKind)[]
 
     /// <summary>Get the locations of format specifiers</summary>
+    [<System.Obsolete("This member has been replaced by GetFormatSpecifierLocationsAndArity, which returns both range and arity of specifiers")>]
     member GetFormatSpecifierLocations : unit -> range[]
 
     /// <summary>Get the locations of and number of arguments associated with format specifiers</summary>