doc: refactor signal info in child_process.md

* Since exec calls execFile and execFile internally calls spawn with
  options.signal, the signal parameter has been documented under exec
  as well.
* Refactored the description of signal under all the functions.
* As the usage of signal has been explained using an example under
  spawn, this removes the rest of the examples as those are very
  similar.

Author: RaisinTen

doc/api/child_process.md

@@ -160,6 +160,8 @@ changes:
   * `shell` {string} Shell to execute the command with. See
     [Shell requirements][] and [Default Windows shell][]. **Default:**
     `'/bin/sh'` on Unix, `process.env.ComSpec` on Windows.
+  * `signal` {AbortSignal} allows aborting the child process using an
+    AbortSignal.
   * `timeout` {number} **Default:** `0`
   * `maxBuffer` {number} Largest amount of data in bytes allowed on stdout or
     stderr. If exceeded, the child process is terminated and any output is
@@ -246,6 +248,9 @@ async function lsExample() {
 lsExample();
 ```
 
+The `signal` option works exactly the same way it does in
+[`child_process.spawn()`][].
+
 ### `child_process.execFile(file[, args][, options][, callback])`
 <!-- YAML
 added: v0.1.91
@@ -280,7 +285,8 @@ changes:
     `'/bin/sh'` on Unix, and `process.env.ComSpec` on Windows. A different
     shell can be specified as a string. See [Shell requirements][] and
     [Default Windows shell][]. **Default:** `false` (no shell).
-  * `signal` {AbortSignal} allows aborting the execFile using an AbortSignal.
+  * `signal` {AbortSignal} allows aborting the child process using an
+    AbortSignal.
 * `callback` {Function} Called with the output when process terminates.
   * `error` {Error}
   * `stdout` {string|Buffer}
@@ -334,18 +340,8 @@ getVersion();
 function. Any input containing shell metacharacters may be used to trigger
 arbitrary command execution.**
 
-If the `signal` option is enabled, calling `.abort()` on the corresponding
-`AbortController` is similar to calling `.kill()` on the child process except
-the error passed to the callback will be an `AbortError`:
-
-```js
-const controller = new AbortController();
-const { signal } = controller;
-const child = execFile('node', ['--version'], { signal }, (error) => {
-  console.log(error); // an AbortError
-});
-controller.abort();
-```
+The `signal` option works exactly the same way it does in
+[`child_process.spawn()`][].
 
 ### `child_process.fork(modulePath[, args][, options])`
 <!-- YAML
@@ -385,7 +381,8 @@ changes:
   * `serialization` {string} Specify the kind of serialization used for sending
     messages between processes. Possible values are `'json'` and `'advanced'`.
     See [Advanced serialization][] for more details. **Default:** `'json'`.
-  * `signal` {AbortSignal} Allows closing the subprocess using an AbortSignal.
+  * `signal` {AbortSignal} Allows closing the child process using an
+    AbortSignal.
   * `killSignal` {string} The signal value to be used when the spawned
     process will be killed by the abort signal. **Default:** `'SIGTERM'`.
   * `silent` {boolean} If `true`, stdin, stdout, and stderr of the child will be
@@ -484,7 +481,8 @@ changes:
     when `shell` is specified and is CMD. **Default:** `false`.
   * `windowsHide` {boolean} Hide the subprocess console window that would
     normally be created on Windows systems. **Default:** `false`.
-  * `signal` {AbortSignal} allows aborting the execFile using an AbortSignal.
+  * `signal` {AbortSignal} allows aborting the child process using an
+    AbortSignal.
   * `killSignal` {string} The signal value to be used when the spawned
     process will be killed by the abort signal. **Default:** `'SIGTERM'`.