doc: remove Returns: {undefined}

Removed * Returns: {undefined} in doc/ to prevent confusing users

PR-URL: nodejs#18951
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

Author: Sho Miyamoto

doc/api/async_hooks.md

@@ -686,8 +686,6 @@ deprecated: v9.6.0
 -->
 > Stability: 0 - Deprecated: Use [`asyncResource.runInAsyncScope()`][] instead.
 
-* Returns: {undefined}
-
 Call all `before` callbacks to notify that a new asynchronous execution context
 is being entered. If nested calls to `emitBefore()` are made, the stack of
 `asyncId`s will be tracked and properly unwound.
@@ -704,8 +702,6 @@ deprecated: v9.6.0
 -->
 > Stability: 0 - Deprecated: Use [`asyncResource.runInAsyncScope()`][] instead.
 
-* Returns: {undefined}
-
 Call all `after` callbacks. If nested calls to `emitBefore()` were made, then
 make sure the stack is unwound properly. Otherwise an error will be thrown.
 
@@ -721,8 +717,6 @@ alternative.
 
 #### `asyncResource.emitDestroy()`
 
-* Returns: {undefined}
-
 Call all `destroy` hooks. This should only ever be called once. An error will
 be thrown if it is called more than once. This **must** be manually called. If
 the resource is left to be collected by the GC then the `destroy` hooks will

doc/api/fs.md

@@ -788,7 +788,6 @@ changes:
 
 * `path` {string|Buffer|URL}
 * `mode` {integer} **Default:** `fs.constants.F_OK`
-* Returns: {undefined}
 
 Synchronously tests a user's permissions for the file or directory specified by
 `path`. The `mode` argument is an optional integer that specifies the

doc/api/http2.md

@@ -327,7 +327,6 @@ added: v8.4.0
 * `code` {number} The HTTP/2 error code to send in the final `GOAWAY` frame.
   If unspecified, and `error` is not undefined, the default is `INTERNAL_ERROR`,
   otherwise defaults to `NO_ERROR`.
-* Returns: {undefined}
 
 Immediately terminates the `Http2Session` and the associated `net.Socket` or
 `tls.TLSSocket`.
@@ -470,7 +469,6 @@ added: v8.4.0
 
 * `msecs` {number}
 * `callback` {Function}
-* Returns: {undefined}
 
 Used to set a callback function that is called when there is no activity on
 the `Http2Session` after `msecs` milliseconds. The given `callback` is
@@ -530,7 +528,6 @@ added: v8.4.0
 -->
 
 * `settings` {HTTP2 Settings Object}
-* Returns {undefined}
 
 Updates the current local settings for this `Http2Session` and sends a new
 `SETTINGS` frame to the connected HTTP/2 peer.
@@ -882,7 +879,6 @@ added: v8.4.0
   `http2.constants.NGHTTP2_NO_ERROR` (`0x00`)
 * `callback` {Function} An optional function registered to listen for the
   `'close'` event.
-* Returns: {undefined}
 
 Closes the `Http2Stream` instance by sending an `RST_STREAM` frame to the
 connected HTTP/2 peer.
@@ -933,7 +929,6 @@ added: v8.4.0
     and `256` (inclusive).
   * `silent` {boolean} When `true`, changes the priority locally without
     sending a `PRIORITY` frame to the connected peer.
-* Returns: {undefined}
 
 Updates the priority for this `Http2Stream` instance.
 
@@ -994,7 +989,6 @@ added: v8.4.0
 
 * `msecs` {number}
 * `callback` {Function}
-* Returns: {undefined}
 
 ```js
 const http2 = require('http2');
@@ -1117,7 +1111,6 @@ added: v8.4.0
 -->
 
 * `headers` {HTTP2 Headers Object}
-* Returns: {undefined}
 
 Sends an additional informational `HEADERS` frame to the connected HTTP/2 peer.
 
@@ -1161,7 +1154,6 @@ added: v8.4.0
   * `pushStream` {ServerHttp2Stream} The returned pushStream object.
   * `headers` {HTTP2 Headers Object} Headers object the pushStream was
   initiated with.
-* Returns: {undefined}
 
 Initiates a push stream. The callback is invoked with the new `Http2Stream`
 instance created for the push stream passed as the second argument, or an
@@ -1196,7 +1188,6 @@ added: v8.4.0
     include payload data.
   * `getTrailers` {Function} Callback function invoked to collect trailer
     headers.
-* Returns: {undefined}
 
 ```js
 const http2 = require('http2');