doc: remove duplicate words in API docs

PR-URL: #17937
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>

doc/api/child_process.md

@@ -623,7 +623,7 @@ pipes between the parent and child. The value is one of the following:
  have an underlying descriptor (file streams do not until the `'open'`
  event has occurred).
 5. Positive integer - The integer value is interpreted as a file descriptor
- that is is currently open in the parent process. It is shared with the child
+ that is currently open in the parent process. It is shared with the child
  process, similar to how {Stream} objects can be shared.
 6. `null`, `undefined` - Use default value. For stdio fds 0, 1, and 2 (in other
  words, stdin, stdout, and stderr) a pipe is created. For fd 3 and up, the

doc/api/perf_hooks.md

@@ -125,12 +125,12 @@ Creates a new `PerformanceMeasure` entry in the Performance Timeline. A
 `startMark` and `endMark`.
 
 The `startMark` argument may identify any *existing* `PerformanceMark` in the
-the Performance Timeline, or *may* identify any of the timestamp properties
+Performance Timeline, or *may* identify any of the timestamp properties
 provided by the `PerformanceNodeTiming` class. If the named `startMark` does
 not exist, then `startMark` is set to [`timeOrigin`][] by default.
 
 The `endMark` argument must identify any *existing* `PerformanceMark` in the
-the Performance Timeline or any of the timestamp properties provided by the
+Performance Timeline or any of the timestamp properties provided by the
 `PerformanceNodeTiming` class. If the named `endMark` does not exist, an
 error will be thrown.