Revert Digest::Class method changes

The original definition allows for flexible behavior in subclasses,
but it can also lead to overlooking issues that should be discovered.
If we want to increase the number of arguments in a subclass,
we should write an overload in that class.

```
Digest::SHA256.base64digest("aaa", :bbb) #=> ArgumentError
```

ref: #2967

Author: ksss

stdlib/digest/0/digest.rbs

@@ -319,15 +319,15 @@ class Digest::Class
   # Returns the base64 encoded hash value of a given *string*.  The return value
   # is properly padded with '=' and contains no line feeds.
   #
-  def self.base64digest: (string str, *untyped args) -> String
+  def self.base64digest: (string str) -> String
 
   # <!--
   #   rdoc-file=ext/digest/bubblebabble/bubblebabble.c
   #   - Digest::Class.bubblebabble(string, ...) -> hash_string
   # -->
   # Returns the BubbleBabble encoded hash value of a given *string*.
   #
-  def self.bubblebabble: (string, *untyped) -> String
+  def self.bubblebabble: (string) -> String
 
   # <!--
   #   rdoc-file=ext/digest/digest.c
@@ -338,7 +338,7 @@ class Digest::Class
   # any, are passed through to the constructor and the *string* is passed to
   # #digest().
   #
-  def self.digest: (string, *untyped) -> String
+  def self.digest: (string) -> String
 
   # <!--
   #   rdoc-file=ext/digest/lib/digest.rb
@@ -350,7 +350,7 @@ class Digest::Class
   #     p Digest::SHA256.file("X11R6.8.2-src.tar.bz2").hexdigest
   #     # => "f02e3c85572dc9ad7cb77c2a638e3be24cc1b5bea9fdbb0b0299c9668475c534"
   #
-  def self.file: (string name, *untyped args) -> instance
+  def self.file: (string name) -> instance
 
   # <!--
   #   rdoc-file=ext/digest/digest.c
@@ -359,7 +359,7 @@ class Digest::Class
   # Returns the hex-encoded hash value of a given *string*.  This is almost
   # equivalent to Digest.hexencode(Digest::Class.new(*parameters).digest(string)).
   #
-  def self.hexdigest: (string, *untyped) -> String
+  def self.hexdigest: (string) -> String
 
   private