Remove out keyword documentation (#50)

Author: kgryte

spec/API_specification/index.rst

@@ -12,7 +12,6 @@ API specification
    type_promotion
    casting
    broadcasting
-   out_keyword
    creation_functions
    elementwise_functions
    statistical_functions

spec/API_specification/out_keyword.md

@@ -6,7 +6,6 @@ A conforming implementation of the array API standard must provide and support t
 
 -   Positional parameters must be [positional-only](https://www.python.org/dev/peps/pep-0570/) parameters. Positional-only parameters have no externally-usable name. When a function accepting positional-only parameters is called, positional arguments are mapped to these parameters based solely on their order.
 -   Optional parameters must be [keyword-only](https://www.python.org/dev/peps/pep-3102/) arguments.
--   The `out` keyword argument must follow the conventions defined in :ref:`out-keyword`.
 -   Broadcasting semantics must follow the semantics defined in :ref:`broadcasting`.
 -   Unless stated otherwise, functions must support the data types defined in :ref:`data-types`.
 -   Unless stated otherwise, functions must adhere to the type promotion rules defined in :ref:`type-promotion`.