[3.12] gh-110393: Remove watchdog with hardcoded timeout (GH-110400) (#110445)

gh-110393: Remove watchdog with hardcoded timeout (GH-110400)

test_builtin and test_socketserver no longer use signal.alarm() to
implement a watchdog with a hardcoded timeout (2 and 60 seconds).
Python test runner regrtest has two watchdogs: faulthandler and
timeout on running worker processes. Tests using short hardcoded
timeout can fail on slowest buildbots just because the timeout is too
short.
(cherry picked from commit 1328fa31fe9c72748fc6fd11d017c82aafd48a49)

Co-authored-by: Victor Stinner <vstinner@python.org>