use self? to express singleton and instance method

stdlib/timeout/0/timeout.rbs

@@ -51,38 +51,7 @@ module Timeout
   # Timeout` into your classes so they have a #timeout method, as well as a module
   # method, so you can call it directly as Timeout.timeout().
   #
-  def self.timeout: (Numeric? sec, ?singleton(Exception) klass, ?String message) { (Numeric sec) -> untyped } -> untyped
-
-  private
-
-  # Perform an operation in a block, raising an error if it takes longer than
-  # `sec` seconds to complete.
-  #
-  # `sec`
-  # :   Number of seconds to wait for the block to terminate. Any number may be
-  #     used, including Floats to specify fractional seconds. A value of 0 or
-  #     `nil` will execute the block without any timeout.
-  # `klass`
-  # :   Exception Class to raise if the block fails to terminate in `sec` seconds.
-  #      Omitting will use the default, Timeout::Error
-  # `message`
-  # :   Error message to raise with Exception Class. Omitting will use the
-  #     default, "execution expired"
-  #
-  #
-  # Returns the result of the block **if** the block completed before `sec`
-  # seconds, otherwise throws an exception, based on the value of `klass`.
-  #
-  # The exception thrown to terminate the given block cannot be rescued inside the
-  # block unless `klass` is given explicitly. However, the block can use ensure to
-  # prevent the handling of the exception.  For that reason, this method cannot be
-  # relied on to enforce timeouts for untrusted blocks.
-  #
-  # Note that this is both a method of module Timeout, so you can `include
-  # Timeout` into your classes so they have a #timeout method, as well as a module
-  # method, so you can call it directly as Timeout.timeout().
-  #
-  def timeout: (Numeric? sec, ?singleton(Exception) klass, ?String message) { (Numeric sec) -> untyped } -> untyped
+  def self?.timeout: (Numeric? sec, ?singleton(Exception) klass, ?String message) { (Numeric sec) -> untyped } -> untyped
 end
 
 Timeout::VERSION: String