gh-97669: Remove Tools/scripts/startuptime.py (#98214)

The "pyperf command" tool be used instead. Example:

    $ python3 -m pyperf command -- python3 -c pass
    .....................
    command: Mean +- std dev: 17.8 ms +- 0.4 ms

pyperf also computes the standard deviation which gives an idea of
the benchmark looks reliable or not.