closes bpo-39135: Remove 'time.clock()' mention in docs. (GH17709)

`time.clock()` was removed in Python 3.8, but it was still mentioned
in the documentation for when `time.get_clock_info()` is given the
argument `'clock'`. This commit removes that mention.

Doc/library/time.rst

@@ -218,7 +218,6 @@ Functions
    Supported clock names and the corresponding functions to read their value
    are:
 
-   * ``'clock'``: :func:`time.clock`
    * ``'monotonic'``: :func:`time.monotonic`
    * ``'perf_counter'``: :func:`time.perf_counter`
    * ``'process_time'``: :func:`time.process_time`