Revert "Add missing US spellings for “scale_grey” (#4299)" (#4411)

Author: thomasp85

R/zxx.r

@@ -192,16 +192,6 @@ scale_color_stepsn <- scale_colour_stepsn
 #' @usage NULL
 scale_color_grey <- scale_colour_grey
 
-#' @export
-#' @rdname scale_grey
-#' @usage NULL
-scale_color_gray <- scale_colour_grey
-
-#' @export
-#' @rdname scale_grey
-#' @usage NULL
-scale_fill_gray <- scale_fill_grey
-
 #' @export
 #' @rdname scale_hue
 #' @usage NULL