Remove proxy.config.ssl.number.threads remnants.

angler:trafficserver.git jpeach$ git grep proxy.config.ssl.number.threads
ci/jenkins/ats_conf.pl:$recedit->set(conf => "proxy.config.ssl.number.threads", val => "8");
ci/tsqa/tests/test_keepalive.py:        cls.configs['records.config']['CONFIG']['proxy.config.ssl.number.threads'] = -1
ci/tsqa/tests/test_keepalive.py:        cls.configs['records.config']['CONFIG']['proxy.config.ssl.number.threads'] = -1
doc/admin-guide/files/records.config.en.rst:.. ts:cv:: CONFIG proxy.config.ssl.number.threads INT -1
lib/perl/lib/Apache/TS/AdminClient.pm: proxy.config.ssl.number.threads
proxy/config/records.config.default.in:CONFIG proxy.config.ssl.number.threads INT -1