CCInt64(cleanup): remove function always present on 4.08

Author: FardaleM

src/core/CCInt64.ml

@@ -126,7 +126,6 @@ let random_range i j st = add i (random (sub j i) st)
 
 let of_string_exn = of_string
 let of_string x = try Some (of_string_exn x) with Failure _ -> None
-let of_string_opt = of_string
 let most_significant_bit = logxor (neg 1L) (shift_right_logical (neg 1L) 1)
 
 type output = char -> unit

src/core/CCInt64.mli

@@ -86,10 +86,6 @@ val of_string : string -> t option
 (** [of_string s] is the safe version of {!of_string_exn}.
     Like {!of_string_exn}, but return [None] instead of raising. *)
 
-val of_string_opt : string -> t option
-(** [of_string_opt s] is an alias to {!of_string}.
-    @since 2.1 *)
-
 val of_string_exn : string -> t
 (** [of_string_exn s] converts the given string [s] into a 64-bit integer.
     Alias to {!Int64.of_string}.