Remove reminiscent trace of Base48.

A long time ago we were using a custom Base48 encoding instead of the
standard Base58.

src/proto/alpha/docs/language.md

@@ -1449,7 +1449,7 @@ All domain specific constants are Micheline strings with specific formats:
     line interface and cannot be forged by hand so their format is of
     no interest here.
   - `key`s are `Sha256` hashes of `ed25519` public keys encoded in
-    `base48` format with the following custom alphabet:
+    `base58` format with the following custom alphabet:
     `"eXMNE9qvHPQDdcFx5J86rT7VRm2atAypGhgLfbS3CKjnksB4"`.
   - `signature`s are `ed25519` signatures as a series of hex-encoded bytes.
 

src/utils/base58.mli

@@ -91,7 +91,7 @@ val complete: ?alphabet:Alphabet.t -> string -> string list Lwt.t
 
 (** {1 Low-level: distinct registering function for economic protocol} *)
 
-(** See [src/proto/environment/base48.mli]} for an inlined
+(** See [src/environment/v1/base58.mli]} for an inlined
     documentation. *)
 module Make(C: sig type context end) : sig